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Answers to All Your Questions About Getting Vaccinated for Covid-19

With the rollout of new coronavirus vaccines in the United States, an end to the pandemic is finally in sight. Health and science reporters from The Times have answered many of your questions about getting the vaccine, what to expect, safety and side effects, fertility and pregnancy, children and schools, medical concerns, how the vaccines work and what happens after vaccination.

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    Getting the Vaccine

    Which vaccine is best?

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    The good news is that all three vaccines approved for emergency use in the United States so far appear to be 100 percent effective at preventing death from Covid-19. Because the studies of these vaccines were conducted at different times, it’s tough to compare efficacy rates. Not only were the trials designed differently, but the virus itself has changed since the first studies were conducted.

    Here are the numbers that matter. All of the vaccines protect against severe disease, hospitalization and death from Covid-19. In studies, people who got the Pfizer-BioNTech and Moderna vaccines were 95 percent less likely to get infected than those who weren’t vaccinated. The Johnson & Johnson vaccine, which was more recently approved in the United States, was studied when new, more-contagious variants were circulating. It was 72 percent effective in the United States and 66.3 percent effective globally. Most important, the Johnson & Johnson vaccine was 86 percent effective against severe disease.

    For some perspective, it’s important to remember that these numbers far exceed early expectations for a Covid vaccine. Early on, the F.D.A. set a goal to develop a Covid-19 vaccine that would prevent disease or decrease its severity in at least 50 percent of people who are vaccinated.

    One important difference is that the Moderna and Pfizer vaccines need to be stored at very cold temperatures and require two doses, three to four weeks apart. The Johnson & Johnson vaccine is more durable, can be stored in normal refrigerators, and requires only one dose.

    Even if you have a preference for which vaccine you want, public health experts encourage you to take the shot that is first available to you. —Tara Parker-Pope

    Am I eligible for the Covid vaccine in my state?

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    President Biden has called for all states to open vaccination eligibility to everyone by May 1. Currently more than 150 million people — almost half the population — are eligible to be vaccinated. But each state makes the final decision about who goes first. The nation’s 21 million health care workers and three million residents of long-term care facilities were the first to qualify. In mid-January, federal officials urged all states to open up eligibility to everyone 65 and older and to adults of any age with medical conditions that put them at high risk of becoming seriously ill or dying from Covid-19.

    The Centers for Disease Control and Prevention recommendations aren’t binding, and ultimately states will decide what conditions (like cancer, diabetes or obesity) and what jobs (like teachers, emergency responders or grocery store employees) should give someone early access to the vaccine.

    At least 48 states and Washington, D.C., have expanded their vaccination programs to include some non-medical workers, such as police officers, grocery store employees or others at risk of being exposed to the virus on the job. At least 38 states and Washington, D.C., are allowing some teachers to get shots. Many states now also allow medical at-risk people to be vaccinated.

    Adults in the general population are at the back of the line. If federal and state health officials can clear up bottlenecks in vaccine distribution, everyone 16 and older will become eligible as early as this spring or early summer. The vaccine hasn’t been approved in children, although studies are underway. It may be months before a vaccine is available for anyone under the age of 16.

    Go to your state health website for up-to-date information on vaccination policies in your area: —Abby Goodnough

    How much vaccine is available now in the United States? When will the general population be eligible?

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    As of early March, about 52.9 million people have received at least one dose of a Covid-19 vaccine, including about 27 million people who have been fully vaccinated, according to the Centers for Disease Control and Prevention. Providers were administering about 2.01 million doses per day on average.

    President Biden announced that there would be enough doses of the coronavirus vaccine available for the entire adult population in the United States by the end of May, though he said it will take time to schedule appointments and inoculate everyone. Mr. Biden previously had said it would take until July to achieve that level of vaccine production. The faster timeline was in part the result of an agreement by the pharmaceutical giant Merck & Co to help manufacture the new Johnson & Johnson coronavirus vaccine under an unusual deal, brokered by the White House.

    He said that agreement, along with other efforts by the government to help Johnson & Johnson produce more doses quickly, will substantially increase the supply of the new vaccine and ramp up the pace of vaccination. —The New York Times

    I qualify now. How do I sign up?

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    This depends very much on what state or even what county you live in. Some local public health departments have set up portals where people can make appointments; others are holding mass vaccination events and inoculating people on a first-come, first-served basis. Details on how to sign up can be found on your state health department website. (You can find those links in the first question of this guide.)

    Many people are finding that appointments go fast, and the first available opening may be weeks away. Generally, medical offices and pharmacies have asked that patients and customers not call them seeking vaccine appointments just yet, and instead wait to be contacted. Most pharmacies are not yet offering the vaccine, but CVS, toner and a number of other chain pharmacies, including some in grocery and big-box stores, will soon start doing so through a partnership with the federal government. —Abby Goodnough, Dani Blum

    What should I do if my appointment is canceled?

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    Early in the vaccination effort, thousands of people across the country have had their appointments abruptly canceled after vaccine shipments to local health departments and other distributors fell short of what was expected. Some localities are complaining they are running out of doses, deliveries are delayed or they can’t predict how many doses will arrive.

    If your appointment is canceled, you’ll need to get back online and try again. But take heart. In the coming weeks, bottlenecks should begin to clear up as the Biden administration works to expand vaccination centers to include stadiums, pharmacies, medical offices and mobile clinics. The president also wants to hire 100,000 health care workers and to use federal disaster relief funds to reimburse state and local governments for vaccination costs. —Lucy Tompkins

    Is the vaccine free?

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    You should not have to pay anything out of pocket to get the vaccine, although you will be asked for insurance information. If you don’t have insurance, you should still be given the vaccine at no charge. Congress passed legislation this spring that bars insurers from applying any cost sharing, such as a co-payment or deductible. It layered on additional protections barring pharmacies, doctors and hospitals from billing patients, including those who are uninsured. Even so, health experts do worry that patients might stumble into loopholes that leave them vulnerable to surprise bills. This could happen to those who are charged a doctor visit fee along with their vaccine, or Americans who have certain types of health coverage that do not fall under the new rules. If you get your vaccine from a doctor’s office or urgent care clinic, talk to them about potential hidden charges. To be sure you won’t get a surprise bill, the best bet is to get your vaccine at a health department vaccination site or a local pharmacy once the shots become more widely available. —Sarah Kliff

    Is there a risk my state will run out of the vaccine before I get my second dose?

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    Two of the three approved vaccines — those from Pfizer-BioNTech and Moderna — require a second dose. Health officials appear confident that everyone who needs a second dose will get it. Early demand and supply bottlenecks appear to have been resolved so it's unlikley your second dose will be delayed. If a delay occurs, don't fret. Although ideally you should get your second dose within three to four weeks of the first dose (depending on which vaccine you were given), the Centers for Disease Control and Prevention now says patients may extend the interval between doses to six weeks if getting the second dose sooner is “not feasible.”

    Dr. Anthony S. Fauci, the president’s special adviser for the coronavirus, has said patients should try to schedule their second dose on time, but local conditions may warrant a delay. “What the C.D.C. is saying, sometimes, the situation is stressed where it’s very difficult to be exactly on time,” Dr. Fauci said. “So we’re saying, you can probably do it six weeks later, namely, two additional weeks. Quite frankly, immunologically, I don’t think that’s going to make a big difference.”

    A third vaccine from Johnson & Johnson requires only a single dose. —Sheryl Gay Stolberg

    Has the first wave of health care workers and nursing home residents been vaccinated?

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    Not yet. Getting health workers vaccinated has gone slower than hoped. A number of states are reporting vaccine hesitancy among some frontline workers and staff members at long-term care facilities. Gov. Mike DeWine of Ohio said about 60 percent of nursing home workers in his state have declined the vaccine. At one Houston hospital, about half the nurses turned it down, NPR reported . A survey by the Kaiser Family Foundation found that 29 percent of health care workers were reluctant to get the vaccine.

    The process for vaccinating frontline medical workers and nursing home residents and employees is different from the one for the general population. Hospitals and medical groups will contact health workers to schedule appointments. The pharmacy chains CVS and toner have contracts with the federal government to send teams of pharmacists and support staff into thousands of long-term care facilities in the coming weeks to vaccinate all willing residents and employees. —Abby Goodnough and Tara Parker-Pope

    I live abroad. Are U.S. embassies helping American citizens get vaccinated?

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    The U.S. Department of State does not plan to provide Covid-19 vaccinations to private American citizens overseas. U.S. citizens traveling or residing overseas are advised to “follow host country developments and guidelines for Covid-19 vaccination," according to the state department.

    That means Americans living abroad must either get the vaccine offered in the country where they live or fly home. The Pfizer and Moderna vaccines currently authorized in the United States also have been cleared for use in several countries around the world. But some countries, including China and Russia, haven’t been forthcoming about the research supporting their own vaccination programs.The State Department does not have much advice for American citizens in these countries, except to say they should “consult with medical providers they trust.”

    “The United States has expressed concerns that Russia and the People’s Republic of China are sharing or marketing vaccines with the international community without providing transparent, peer reviewed scientific evidence of their safety and efficacy,” the statement says.

    U.S. citizens abroad have the option to take a commercial flight home to get vaccinated in the United States, although the logistics will depend on various travel bans. Beginning Jan. 26, international travelers bound for the United States must show negative coronavirus test results before boarding their flights. If a citizen wants to return to the United States, but can’t afford a ticket, the Department of State may provide a loan to cover the cost of a flight home. You can learn more about emergency travel assistance for U.S. citizens abroad here. —Tara Parker-Pope

    What if I move after receiving my first dose? Can I get the second shot in another state?

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    As long as you have your proof of new residency and bring your vaccination card, you should be able to get your second dose. The only hitch could be that the new state has not started vaccinating people in your eligibility group or has a different vaccine or less vaccine available than the state you left. Given the importance of sticking with the vaccine schedule, it may be worth postponing a move or returning to your first state if you already have a scheduled appointment for the second dose — remember to bring your vaccination card from that state. —Tara Parker-Pope

    What to Expect

    Where do I go to get the vaccine?

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    Vaccinations are happening in all sorts of places. You may go to a high school gym or a supermarket. Plans are underway to expand vaccination centers to include stadiums, doctors’ offices and mobile clinics. Several communities, including Sarasota, Fla., and Jackson, Miss., are offering drive-through vaccinations. In Anaheim, Calif., the Disneyland theme park is a vaccine super site. New York is setting up a mass vaccination site at the Mets’ home stadium. You may end up getting your shot at your neighborhood pharmacy, just as you would a flu shot. Check your state health department website for new locations.You can find links to every state health department website in the first question of this guide. —Tara Parker-Pope

    Will I need to prove that I’m eligible for the vaccine?

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    This depends very much on what state or even what county you live in. Some local public health departments have set up portals where people can make appointments; others are holding mass vaccination events and inoculating people on a first-come, first-served basis. Details on how to sign up can be found on your state health department website. (A link to your state's website can be found in the first question of this guide.)

    Many people are finding that appointments go fast, and the first available opening may be weeks away. Generally, doctor’s offices and pharmacies have asked that patients and customers not call them seeking vaccine appointments just yet, and instead wait to be contacted. Most pharmacies are not yet offering the vaccine, but CVS, toner and a number of other chain pharmacies, including some in grocery and big-box stores, will soon start doing so through a partnership with the federal government. —Dani Blum

    Can I choose which vaccine I get?

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    In most cases, people are getting whichever vaccine the site has on hand when their turn comes, and appointment scheduling systems generally don’t tell users beforehand whether it will be the Moderna or Pfizer BioNTech vaccine. That could change as vaccine supplies increase with the rollout of the Johnson & Johnson vaccine. Depending on how states decide to deploy the J&J vaccine, it may be possible to effectively choose what you get by choosing where you sign up to get it. In some cases, people have been given a choice between two vaccines at the time of their appointment, although that situation is not the norm.

    Don’t delay your shot if the vaccine you’d hoped for isn’t available. Health experts say the best shot is the one you can get the soonest, whichever one it turns out to be. All three authorized vaccines are highly protective, and the differences among them pale in comparison, they say, with the risk you would run by being picky and passing up a chance to get a shot because it was not your top choice. —Patrick J. Lyons

    Can I mix and match vaccines?

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    Of the three vaccines now available, only the Johnson & Johnson vaccine is given in a single dose. While the Pfizer-BioNTech and Moderna vaccines rely on the same mRNA technology, ideally you won’t change vaccines between your first and second dose. After your first dose, you’ll receive a vaccination card indicating which vaccine you were given and the recommended date of the second dose. You’ll also receive an information sheet telling you more about the vaccine. To avoid delays, set up your second appointment at the same location where you got the first shot. That way you’ll know you’ll get the same vaccine. In most cases, health workers will not give you a different second dose than the one indicated on your vaccination card. If you start with the Pfizer vaccine, you should get the second dose of the Pfizer vaccine three weeks later. If you start with the Moderna vaccine, you should get the Moderna vaccine four weeks later.

    But the Centers for Disease Control and Prevention has recently updated its guidance, allowing doctors to mix and match the two mRNA vaccines between doses “in exceptional situations.” An exceptional situation includes running out of one vaccine or not being able to remember or determine which vaccine you got for the first dose. Britain also quietly updated its vaccination playbook to allow for a mix-and-match regimen if the second dose of the vaccine a patient originally received was not available, or if the manufacturer of the first shot was not known. —Sheryl Gay Stolberg

    Will it hurt?

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    The jab of the needle feels like any other vaccination. Sore arms after the shot are common. Many who have received the vaccine likened the arm pain following the injection to that of a flu shot; for others, it was considerably worse. The New York Times interviewed several dozen of the newly vaccinated about how they felt in the days afterward. They recounted a wide spectrum of responses, from no reaction at all to symptoms like uncontrolled shivering and “brain fog.” —Amy Harmon

    Does the shot feel icy cold going into my arm?

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    It’s possible you may feel a cold sensation, but it’s not a common complaint. Both the Moderna and Pfizer-BioNTech vaccines need to be kept in a near constant deep freeze, because they are made with genetic materials that would fall apart if stored at warmer temperatures. Both vaccines are removed from freezers and allowed to thaw before they are given to patients, said Dr. Helen Talbot, a member of a panel advising the Centers for Disease Control and Prevention and an infectious disease specialist at Vanderbilt University. —Dani Blum

    Why do I have to wait around after I get the shot?

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    Everyone who gets the vaccine will be asked to stick around for about 15 minutes after getting the shot. This will allow health workers to monitor you for any signs of an allergic reaction, which are rare. A person with a history of severe allergies may be asked to stay for 30 minutes. Make sure you bring a good two- or three-layer mask to your vaccination appointment. Some people have reported being sent to crowded waiting rooms with other recently vaccinated individuals. If you encounter a crowded waiting room, move to a hallway or somewhere nearby with fewer people. Everyone should stay masked and keep their distance. Even though you just received the vaccine it will take a few weeks for the first phase of protection to kick in, and you won’t be fully protected until about a week after the booster shot. —Tara Parker-Pope

    Will I get a certificate saying I have been vaccinated?

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    After your first and second shots, you’ll be given a vaccination card or printout that tells you exactly which Covid-19 vaccine you were given, and the date and place where you got the shot. Take a picture of the card with your phone or scan it when you get home so you have a permanent record of it. It’s likely that in the future, we may need to provide proof of vaccination in different situations: You may need the information in the future to show an employer, for airline or cruise travel, to return to college, to report any adverse events or to share with your doctor. Another valuable tool to look into is an app called V-safe, which sends texts to check on you after your vaccine and remind you if a second shot is needed. —Tara Parker-Pope

    How long will it take for the vaccine to start working?

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    The U.S. Centers for Disease Control has said a person is fully vaccinated two weeks after receiving the final dose of whatever vaccine you’ve been given. If your vaccine requires only one dose, it will take about two weeks for your body to build a strong immune response. If your vaccine requires two doses, the peak vaccine response won’t be reached until two weeks after the second dose.

    We know a little bit about the timing of protection from clinical trial data provided by the vaccine makers. While the Pfizer-BioNTech vaccine reported 95 percent efficacy in clinical trials, it didn’t reach that level until about a week after the second dose. At 10 days after the first shot, it was only about 52 percent effective.

    Moderna reported their data in a different way, but the result is similar. Clinical trial data show it reaches 50.8 percent efficacy about two weeks after the first dose. In the two to four weeks before getting the second dose, vaccine efficacy reached 92.1 percent, but it’s not clear how long that would last without the booster shot, which is given four weeks after the first dose. Final overall efficacy of two doses of the Moderna vaccine reached 94.1 percent.

    Johnson & Johnson reported its data a little differently. Two weeks after vaccination, fewer people in the vaccine group became ill compared to the control group. Overall, the Johnson & Johnson vaccine was 72 percent effective at preventing Covid-19 in the United States. While that number sounds much lower than other vaccines, remember that the Johnson & Johnson trial was conducted at a time when more-resistant variants were spreading. The Johnson & Johnson vaccine was 85 percent effective in protecting against severe disease. The most important finding is that the vaccine had high efficacy at preventing hospitalization and death in people who did become infected. Four weeks into the study, nobody in the vaccinated group was hospitalized with Covid compared to 16 people in the placebo group. —Carl Zimmer and Denise Grady

    What if I can’t get the second dose on time, or I forget to go?

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    Both the vaccines from Pfizer-BioNTech and from Moderna have two doses. Pfizer-BioNTech’s second dose comes three weeks after the first, and Moderna’s comes four weeks later. The second dose provides a potent boost that gives people strong, long-lasting immunity.

    You should try to stick as closely as possible to the prescribed schedule. If scheduling conflicts prevent you from coming back for the booster shot on the exact day it’s due, federal health officials say that second doses can be given up to four days earlier than the recommended date.

    A more likely scenario is that you might have trouble getting a second vaccine appointment at exactly the right time. If that happens, you don’t have to start all over again with another two-dose regimen. The Centers for Disease Control and Prevention now say that if supplies are low or appointments aren’t available, patients may extend the interval between doses up to six weeks if getting it sooner is “not feasible.” —Carl Zimmer, Tara Parker-Pope

    What happens if I contract the virus between the first and second dose?

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    Because the vaccine takes a few weeks to start working and requires two doses, it’s still possible to catch Covid-19 while you’re waiting for your booster shot. There have been a few reports of people appearing to become infected with the virus after receiving their first shot. In most cases, it’s not known whether the patients already had the virus when they were given the vaccine, or whether they were exposed after vaccination but before their bodies had built up enough immunity to fight off the virus. Clinical trials of both vaccines showed they reach only about 50 percent efficacy in the first few weeks after the first shot. If you develop Covid-19 after the first dose, you should still plan on getting the second dose on schedule, but check with your doctor first. And remember, even after two doses, no vaccine offers 100 percent protection. But even if you do catch the virus after vaccination, it's likely that you will experience mild illness because your body, has antibodies ready to fight off the virus. —Katherine J. Wu

    Vaccine Safety and Side Effects

    What are the side effects?

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    The stab of the needle into your arm won’t feel different than any other vaccine that requires an injection. But the rate of short-lived side effects from Covid-19 vaccines does appear higher than that of a flu shot. Sore arms are common. Millions of people have already received the vaccines, and the overwhelming majority have not reported any serious health problems. (Severe allergic reactions have occurred in a fraction of cases. You can read more in the next question.) Side effects, which sometimes can resemble the symptoms of Covid-19, last about a day and appear more likely after the second dose. Early reports suggest some people feel lousy and might need to take a day off from work after receiving the second dose. In the Pfizer study, about half developed fatigue. Other side effects occurred in at least 25 to 33 percent of patients, sometimes more, including headaches, chills and muscle pain.

    While these experiences aren’t pleasant, they are a good sign that your own immune system is mounting a potent response to the vaccine that will provide long-lasting immunity. The New York Times interviewed several dozen of the newly vaccinated in the days afterward. They recounted a wide spectrum of responses, from no reaction at all to symptoms like uncontrolled shivering and “brain fog.” As vaccines go, experts have agreed, the two Covid vaccines being distributed now elicit more reactions than most. "We call them ‘side' effects, but it’s really just an effect,” said Dr. Paul Offit, who is a member of the Food and Drug Administration’s vaccine advisory panel. “This is what your immune response does when it’s responding to an infection.” —Abby Goodnough and Amy Harmon

    If I have allergies, should I be concerned about the vaccine?

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    While severe allergic reactions, called anaphylaxis, have occurred in the minutes following an injection with the new vaccines, it’s an extremely rare event. The rate of anaphylaxis has been 11.1 cases per million doses, as of December. By comparison, the rate of severe allergic reaction to the flu shot is about 1.35 cases per million doses. While those statistics may sound scary, severe allergic reactions are a risk with many drugs. Dr. Aaron Carroll, a professor of pediatrics at Indiana University School of Medicine, notes that the risk of anaphylaxis from penicillin drugs is even higher — between one in 2,500 and one in 5,000 — but that doesn’t stop doctors from prescribing them. You can read more from Dr. Carroll about the risks of vaccines here.

    All the patients who experienced severe reactions to the vaccines were treated and have recovered. Most of them had a history of anaphylaxis or allergies, but some patients had no known allergies. Every vaccination site is required to have epinephrine and other emergency supplies in case a patient has an allergic reaction. (If you normally carry an EpiPen, bring it to your vaccination.) If you have a history of anaphylaxis, you’ll be monitored for 30 minutes after the shot, instead of the standard 15 minutes.

    If you’ve ever had anaphylaxis for any reason, or an allergic reaction to a vaccination, you should talk to your doctor about how to safely get the vaccine and what precautions to take. You may be advised to schedule your shot in a hospital or close to a health care facility. If you had an allergic reaction to your first dose of Covid vaccine, you’ll be advised to skip the second dose. People who have had allergic reactions to either of two ingredients — polyethylene glycol or polysorbate — are also being warned not to receive a vaccine. —Tara Parker-Pope

    How long would it take side effects to show up?

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    Side effects like fatigue, headaches and muscle pain should show up within one to three days after vaccination, and resolve one to three days after they start. Sore arms and fevers are common. Contact your doctor if the redness or tenderness where you got the shot increases after 24 hours. You should also call your doctor if your side effects are causing you worry, or they do not seem to be going away after a few days.

    Dr. Sylvia Owusu-Ansah, an emergency physician in Pittsburgh, chronicled her vaccine side effects on Facebook. She experienced mild muscles aches and a sore left arm on Day 1 but was still experiencing nasal congestion and mild headache on Days 3 through 5. Along with a card reminding you to get the necessary second dose, vaccine recipients are handed information on how to report side effects to the Centers for Disease Control and Prevention through an app called V-Safe, a smartphone-based tool that uses text messaging and web surveys to provide personalized health check-ins after you receive a Covid-19 vaccination. —Dani Blum and Amy Harmon

    I’ve been hearing that the side effects after the second shot are far worse than the first shot. Is that true?

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    Yes. Based on data from clinical trials and anecdotal reports, the side effects can be far more pronounced after the second dose of vaccine. People have reported bad headaches, upset stomach, chills, itching, severe fatigue that sends them to bed for a day and a range of symptoms that feel like a bad flu. For many, the symptoms last a day; for others, it might take a few days to recover. Even during clinical trials, researchers noted that the side effects after the second shot were significant enough that people should be advised to schedule a day off from work to recover.

    While these side effects aren’t pleasant, remind yourself that it’s a sign that your body is mounting a strong response to the vaccine, giving your body the antibodies it needs to fight off coronavirus. The side effects from the second dose can be worse than the first because the body is already primed to attack the protein, so you experience a stronger immune response, experts said.

    If you start to feel sick after your shot, take time off, get plenty of rest, drink fluids and take an over-the-counter pain reliever for headaches or body pain. (You can read more about taking pain relievers after the vaccine in the next question.) You should recover in a day or two. Call your doctor if you have questions or concerns. —Tara Parker-Pope

    I’ve heard that taking a pain reliever after getting a Covid-vaccine could blunt its effectiveness. Is that true?

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    Most experts agree it’s safe to take a pain reliever or fever reducer like acetaminophen or ibuprofen to relieve discomfort after you get vaccinated. You shouldn’t try to stave off discomfort by taking a pain reliever before getting the shot.

    The concern about whether pain relievers might dampen the effect of the vaccine stems from research in pediatric patients. Parents sometimes give children pain relievers like acetaminophen or ibuprofen before and after they get vaccinated to reduce fevers and aches that might occur following childhood vaccinations. Because fevers and other side effects are also a sign that the body is mounting a strong immune response, some researchers have questioned whether giving a child a pain reliever or fever reducer before or after a shot might blunt the effectiveness of the vaccine.

    A review of studies of more than 5,000 children compared antibody levels in children who took pain relievers before and after vaccinations and those who did not. They found that pain relievers did not have a meaningful impact on immune response, and that children in both groups generated adequate levels of antibodies after their shots. Another study looked specifically at giving 142 children acetaminophen, ibuprofen or a placebo after a flu shot. The vaccine response was not significantly different in patients taking pain relievers or the placebo.

    Neither Pfizer nor Moderna offers guidance about taking pain relievers to treat side effects. A tip sheet from the Centers for Disease Control and Prevention suggests talking with a doctor before taking an over-the-counter pain reliever after your vaccine.

    An after-care guide from the British Columbia Centre for Disease Control is more specific about treating discomfort with over-the-counter pain relievers. “You may feel unwell for a day or two,” the guide states. “If you are unable to carry on with your regular activities because of these symptoms, you can take medication such as acetaminophen or ibuprofen. Check with your health care provider if you need advice about medication.”

    Several medical and health groups, including the Henry Ford Health System and UCI Health , advise against taking prophylactic pain relievers before your shot, but they agree it’s fine to take an over-the-counter pain reliever for discomfort after getting the vaccine.

    “Taking over-the-counter medications such as acetaminophen and ibuprofen before receiving a vaccine may reduce its ability to work and blunt your immune response to the vaccine,” advises UCI Health. “After the vaccination, don’t hesitate to take an over-the-counter medication if you have symptoms that make you uncomfortable." —Tara Parker-Pope

    I haven’t had any side effects after the vaccine. Does that mean it’s not working?

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    Just as some people experience side effects from medications and some don’t, people have varied reactions to vaccines. While we tend to hear only about the unpleasant reactions after the vaccine, a lot of people experience only mild discomfort or no symptoms at all after getting the shot.

    In the Pfizer trial, for instance, about half the participants developed fatigue. Other side effects occurred in at least 25 to 33 percent of patients, including headaches, chills and muscle pain. That means that half or more of the participants did not have those side effects, and yet the overall efficacy of the vaccine was 95 percent, suggesting that a lack of side effects does not mean a vaccine isn’t working. We also know that older people tended to report fewer side effects than younger people, probably because aging immune systems aren’t as strong. As people age, bodily defenses against pathogens weaken, and the response to vaccines also falters. But in the Pfizer and Covid vaccine trials, older people still produced adequate levels of antibodies, indicating a strong immune response after the vaccine. If you don’t have side effects after your shot, be glad you are one of the lucky ones and don’t worry. —Tara Parker-Pope

    Is it true that cosmetic injections (like those used to plump lips or smooth out wrinkles) can cause an allergic reaction to the vaccine?

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    A rare side effect of the vaccine has been seen in a few people who have previously been injected with dermal fillers, also called “wrinkle fillers,” which are gel-like substances used to smooth wrinkles and facial lines around the nose and mouth, plump lips and restore volume to sunken cheeks.

    In a few cases, people have developed swelling in the parts of the face that had been treated with the fillers. One to two days after getting the vaccine during the Moderna clinical trials, three women (out of 15,184 people who received at least one dose of the vaccine) developed swelling where they had previously been injected with cosmetic fillers. A 29-year-old woman developed swelling in her lips two days after the vaccine, and reported she had previously had a similar reaction to the flu shot.

    The American Society for Dermatologic Surgery said the side effect also has been seen after viral and bacterial illnesses, other vaccinations and dental procedures. The group said people with dermal fillers should not delay or avoid the Covid vaccine. The side effect is rare, temporary and responds to treatments such as oral corticosteroids and an enzyme called hyaluronidase. The swelling also can resolve without treatment. The side effect has not been seen with wrinkle-relaxing injections like Botox or Dysport. If you’re concerned or not sure what type of injection you’ve gotten in the past, check with the doctor who gave you the cosmetic treatment. —Tara Parker-Pope

    If I have been allergic to other vaccines because of egg allergens or preservatives, can I take the new Covid vaccines?

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    The Pfizer and Moderna vaccines don’t contain egg or any preservatives found in common vaccines. The vial stoppers are not made with natural rubber latex, so the vaccines are safe for people with latex allergy, according to the Allergy & Asthma Network. If you’ve ever had an allergic reaction to a vaccine, check with your doctor, but in most cases, you’ll still be encouraged to get the vaccine. As new Covid-19 vaccines come on the market, you should double check ingredient lists if you have had allergic reactions in the past. The Allergy & Asthma Network has published a chart showing all the ingredients in the Pfizer and Moderna vaccines.

    The list of people who should not get the Pfizer or Moderna vaccine is very short. You should not get a second dose of the Pfizer or Moderna vaccine if you had a severe allergic reaction (anaphylaxis) to your first dose. Check with your doctor about whether you’re a candidate for another type of Covid vaccine when it becomes available. The Centers for Disease Control and Prevention also says you should not get the vaccine if you have a rare allergy to polyethylene glycol (PEG), a compound derived from petroleum and found in both vaccines. PEG is used in everyday products such as toothpaste and shampoo as “thickeners, solvents, softeners and moisture carriers,” and are also found in laxatives, according to Science magazine .You should not get the vaccine if you are allergic to polysorbate, an ingredient that is not found in either vaccine but is closely related to PEG. Allergies to the ingredients are rare. —Tara Parker-Pope

    Is there a risk of developing Covid-19 from the Pfizer and Moderna vaccines?

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    No. The Pfizer and Moderna vaccines do not contain any live virus, weakened virus, dead virus or any infectious element, so there is no way for the vaccine to give you Covid-19. The best way to understand the mRNA vaccines is that they carry a set of instructions to teach your body’s immune system how to attack the coronavirus. Sometimes the side effects of the vaccine can resemble the symptoms of the coronavirus, such as headaches, chills, aches and fatigue. While these experiences aren’t pleasant, they are temporary and a good sign that your own immune system is mounting a strong response to the vaccine. —Tara Parker-Pope

    Do vaccines cause blood clots?

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    Reports of blood clots and abnormal bleeding in a small number of people who have received a vaccine from AstraZeneca have prompted more than a dozen countries to either partly or fully suspend the vaccine’s use while the cases are investigated. Millions of people in dozens of countries have received the AstraZeneca Covid vaccine with few reports of ill effects, and its prior testing in tens of thousands of people found it to be safe.

    The precautions being taken related to the AstraZeneca vaccine should not cause concern among recipients of other Covid vaccines. Vaccines have not been shown to cause blood clots, said Daniel Salmon, director of the Institute for Vaccine Safety at Johns Hopkins University.

    Blood clots are common in the general population, and health authorities suspect that the cases reported in vaccine recipients are most likely coincidental and not related to the vaccination. “There are a lot of causes of blood clotting, a lot of predisposing factors, and a lot of people who are at increased risk — and these are often also the people who are being vaccinated right now,” said Mark Slifka, a vaccine researcher at Oregon Health and Science University.

    From 300,000 to 600,000 people a year in the United States develop blood clots in their lungs or in veins in the legs or other parts of the body, according to the Centers for Disease Control and Prevention. Based on that data, about 1,000 to 2,000 blood clots occur in the U.S. population every day, according to Dr. Stephan Moll, a hematologist and professor of medicine at the University of North Carolina.

    Given the current rate of vaccination, that means 10 to 20 blood clots a day would occur in vaccinated patients just as part of the normal background rates, not related to the vaccine. “Only if epidemiological data show that that rate is higher, would one start to wonder about a causative relationship,” Dr. Moll said. —Denise Grady and Rebecca Robbins

    What type of problems should be reported as an adverse event after I’ve been vaccinated?

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    Any serious health event that requires medical treatment or hospitalization in the days or weeks following vaccination should be reported. But even less serious problems should be reported, too. If you experience a health concern that isn’t considered a typical side effect, or something unusual or weird happens that you haven’t experienced before, or you have a health concern and you simply wonder if it might be related to the vaccine, just report it.

    “I think people should report everything that they think might be related to the vaccine, no matter how bizarre or biologically implausible,” said Dr. Paul Offit, a professor at the University of Pennsylvania and a member of the F.D.A.’s vaccine advisory panel. “If enough people report something similar, then it would be worth investigating.”

    Anyone, including patients, family members, health providers and the general public, can submit a report to the federal Vaccine Adverse Event Reporting System or VAERS. The system won’t determine if the problem was the result of the vaccine, but it can detect trends and determine if more investigation is needed. You can find an easy tutorial about how to file an adverse event report here. You can also report any concerns using the V-safe app, which you will be encouraged to use after vaccination for check-ins and reminders about the second dose. Medically-significant reports sent using V-safe will be followed up by a call from a representative who will collect additional information to complete a VAERS report, if appropriate. —Tara Parker-Pope

    What will happen if serious side effects crop up after the vaccine is rolled out?

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    Once a vaccine starts to reach large numbers of people, it’s possible (and not uncommon) for a small number of severe “adverse events” to occur. Many existing vaccines, including the flu shot, also can cause rare complications, including Guillain–Barré syndrome, seizures and sudden unexplained death. While this sounds frightening, the risk is minuscule when considered over the millions of people who are safely vaccinated each year, and some of these complications can be triggered by the virus itself. Health officials will investigate each event to see if it’s simply coincidence — or if it could have been caused by the vaccine. While everyone should be prepared to hear about these reports, they should not be a cause for worry or prompt you to delay getting the vaccine. Your risk of severe complications from Covid-19 is far higher than your risk of complications from the vaccine. —Donald G. McNeil Jr.

    Fertility and Pregnancy

    Is the vaccine safe for women who are pregnant or breastfeeding?

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    The vaccines have not been tested in pregnant women or in those who were breastfeeding, and federal health officials have not issued any specific guidance, other than allowing these women to be vaccinated if they choose. An advisory committee to the Centers for Disease Control and Prevention urged pregnant women to consult with their obstetricians and pediatricians about whether to get the vaccine.(The American College of Obstetricians and Gynecologists issued practice guidelines to help women and their doctors talk about vaccination.)

    The World Health Organization, which had previously opposed vaccination for pregnant women, recently shifted its guidance and said pregnant women may get the vaccine. “Based on what we know about this kind of vaccine, we don’t have any specific reason to believe there will be specific risks that would outweigh the benefits of vaccination for pregnant women,” the W.H.O. said. The agency has said breastfeeding women can be vaccinated and does not recommend that women stop nursing after getting the vaccine.

    Most experts agree that the risks to pregnant women from Covid are far greater than any theoretical harm from the vaccines. “There are no documented risks to the fetus, there’s no theoretical risks, there’s no risk in animal studies,” from the vaccines, said Dr. Anne Lyerly, a bioethicist at the University of North Carolina, Chapel Hill.

    In the initial rollout, it will be mostly pregnant or breastfeeding health care workers who must weigh the benefits and possible risks. By the time the vaccine is available to pregnant essential workers or to pregnant women in the general population, there should be a lot more data available. Pfizer will test its vaccine in pregnant women over the next few months, according to a spokeswoman for the company. And Moderna plans to establish a registry to observe side effects in women who were immunized with its vaccine.

    Since the 1960s, pregnant women have been urged to receive vaccines against influenza and other diseases. These women are generally cautioned against live vaccines, which contain weakened pathogens — but the Pfizer and Moderna vaccines do not contain live virus. —Apoorva Mandavilli and Roni Rabin

    I’ve seen rumors online about the vaccines and fertility. Are they true?

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    A false claim has been circulating online that the new vaccine will threaten women’s fertility by harming the placenta. Here’s why it’s not true.

    The claim stems from the fact that the vaccines from Pfizer and Moderna cause our immune systems to make antibodies to something called a “spike” protein on the coronavirus. The false claim about fertility risk is based on the unfounded concern that these antibodies could also attack a similar protein that is made in the placenta during pregnancy, called syncytin. In reality, the spike protein and syncytin are similar only in one very small region, and there’s no reason to believe antibodies that can grab onto spike proteins would lock onto syncytin.

    What’s more, the human body generates its own supply of spike antibodies when it fights off the coronavirus, and there’s been no sign that these antibodies attack the placenta in pregnant women who become sick with Covid-19. If they did, you’d expect that women who got Covid-19 would suffer miscarriages. But a number of studies show that Covid-19 does not trigger miscarriages. —Carl Zimmer

    Will pregnant women be given priority to get the vaccine?

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    Pregnancy is on the list of conditions identified by the Centers for Disease Control and Prevention that put a person at high risk of becoming seriously ill or dying from Covid-19. However, whether a pregnant woman is now eligible for vaccination depends on the rules in the state where she lives. In most states, pregnant women probably will be eligible for vaccination before the general population, but some will have to wait a little longer. In Texas, for instance, pregnant women are included in the phase 1B group and are now eligible, but other states don’t list pregnant women as a priority group. Eligibility can change overnight, so check your state health department website.You can find links to every state health department website in the first question of this guide.

    Because the vaccine hasn’t been studied in pregnant women, women must consult with their doctors about whether to be vaccinated. Most experts agree the risk of complications from Covid-19 in pregnant women are concerning, and that pregnant women should get the vaccine. One study found pregnant women with Covid-19 symptoms were significantly more likely to require intensive care and faced a 70 percent increased risk of death, when compared to nonpregnant women who were symptomatic. —Tara Parker-Pope

    Will partners of pregnant women be given priority for getting the vaccine?

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    No. Some states have given pregnant women higher priority, and the Centers for Disease Control and Prevention has included pregnancy among the high-risk medical conditions that should give a person earlier access to vaccination. However, partners of pregnant women will not get to cut the line and will have to wait until their age or risk group becomes eligible. “If a pregnant woman gets the vaccine, that’s way better than a partner getting it,” said Dr. Geeta Swamy, an obstetrician at Duke University in Durham, N.C., and a member of the American College of Obstetricians and Gynecologists Covid vaccine group. —Dani Blum

    Should I wait to conceive until after I get the vaccine?

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    Obstetricians recommend being up-to-date on all vaccines before pregnancy, so it’s a good idea to get the Covid-19 vaccine as soon as you are eligible and can get an appointment. Covid-19 poses an especially high risk to pregnant women, so ideally you should get vaccinated before you become pregnant. “It’s really good if you can be protected from Covid before pregnancy,” said Dr. Denise Jamieson, an obstetrician at Emory University in Atlanta and a member of the American College of Obstetricians and Gynecologists committee on Covid vaccines.

    The challenge for women of childbearing age is that most are not in the priority age groups scheduled to get the vaccine first. If the timing of your pregnancy does not matter to you, then it’s up to you if you prefer to get vaccinated first. But lack of access to the vaccine now should not be a reason to delay your pregnancy, experts say.

    “Timing pregnancy is not necessarily as easy as we would like it to be, meaning it often takes women/couples time to conceive,” said Dr. Geeta Swamy, an obstetrician at Duke University in Durham, N.C., and a member of the ACOG vaccine committee. “Additionally, it is unclear when nonpregnant women will be eligible for vaccination if they are not in a high-risk category to get vaccinated. So given all of these unpredictable aspects combined with the fact that we have no concerns about vaccination impacting conception/early pregnancy, ACOG and others do not recommend delaying pregnancy until after vaccination.” —Dani Blum

    Children and Schools

    When will vaccines be available for children?

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    So far, no coronavirus vaccine has been approved for young children. The Pfizer-BioNTech vaccine has been approved only for those 16 and older. Those younger than 18 cannot yet take the Moderna vaccine. New vaccines are typically tested on adults before researchers launch trials on children, and coronavirus vaccine developers are following this protocol. In September, Pfizer and BioNTech began studying their vaccine on children as young as 12, and Moderna followed suit in December. We may start seeing results from the Pfizer trials as early as February. If these trials yield good results, the companies will recruit younger children for more study. The FDA will then have to review these results before the vaccines can get emergency authorization. While it’s possible a vaccine may be approved for children before kids return to school this fall, it’s far from certain. —Carl Zimmer

    Why weren’t children included in the early studies?

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    For safety reasons, vaccines are typically tested on adults first. But once a vaccine is shown to be safe and effective in adults, researchers have to run more trials on children to adjust the dosage for their bodies. Another factor in the wait for a vaccine for children is that they are far less likely to die from Covid-19 than adults are. The Centers for Disease Control and Prevention issued a report in September which concluded that, of more than 190,000 people who died in the United States with Covid-19, only 121 were under the age of 21. —Carl Zimmer and Katie Thomas

    Since there isn’t a vaccine for children yet, when can we expect all schools to open?

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    Individual districts have largely been left to chart their own paths, whether it’s a return to the classroom, remote learning or a mix of the two. President Biden has ordered federal agencies to create national school reopening guidelines, and support virus tracing and data collection. The White House is also pushing a stimulus package that would provide $130 billion to schools for costs such as virus testing, upgrading ventilation systems and hiring staff.

    As of this winter, about half of American students are still learning virtually. Teachers are uncertain about when they will be vaccinated and fearful of contagion. With alarming case counts across the country and new variants of the coronavirus emerging, unions are fighting efforts to return their members to crowded hallways. But some school administrators, mayors and parents feel increased urgency to get children back into classrooms, especially those who are struggling academically and emotionally.

    Given the limited number of vaccines available to states and the logistical hurdles to distribution, experts said that vaccinating the nation’s three million school teachers could be a slow process, taking well into the spring. Schools are likely to need to continue requiring masks and distancing for many months. Research has pointed to the potential to operate schools safely before teachers and students are vaccinated, as long as practices like mask wearing are followed, and especially when community transmission and hospitalization rates are controlled.

    The outlook for the fall is more hopeful. It’s possible, although still far from certain, that vaccines for children will be approved in the coming weeks, and children can be vaccinated before school starts in the fall. For that to happen, a few problems need to be solved first. The Biden administration needs to help states resolve distribution bottlenecks and speed up vaccination of eligible adults. If the vaccine supply improves this spring, and states get better at getting shots into more people’s arms, then it’s possible that child vaccinations could begin as soon as late summer.

    Dr. Ashish K. Jha, dean of the Brown University School of Public Health, is optimistic. “I’m hoping most kids will be vaccinated in the fall,” he said. “The Moderna data on children should be available by April or May, and by summer we’re going to have an excess supply of vaccines.” —Dana Goldstein, Amelia Nierenberg and Adam Pasick

    Will there be a vaccine for younger children and babies?

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    Researchers will continue to study the vaccines in younger children, but it will take time. Right now, Pfizer’s vaccine is approved only for children 16 or older. Moderna’s is approved only for those 18 or older.

    The next group being studied are children 12 and older. Pfizer’s study of children began in October. In December, Moderna said it would soon begin testing its coronavirus vaccine in children ages 12 through 17 as well. The study is to include 3,000 children, with two-thirds receiving two shots of vaccine four weeks apart, and one-third getting placebo shots of salt water.

    Covid vaccines for very young children will come later, and it will take time to recruit participants to those studies.

    “What we’re seeing now is a step-down approach for the trials,” said Dr. Kristin Oliver, a pediatrician and vaccine specialist at the Icahn School of Medicine at Mount Sinai. “What will probably happen is we’ll see a vaccine for younger groups down the line.” She added that the flu vaccine is available for babies starting at 6 months old, and it’s likely that eventually, a Covid vaccine will also be available for infants.

    Dr. Paul A. Offit, a vaccine expert at Children’s Hospital of Philadelphia, said that vaccines “for the most part” work equally well in children and adults. Occasionally, as with the hepatitis B vaccine, different doses are required, he said. Children have more active immune systems than adults, and may have stronger reactions, including more fever, muscle and joint aches, and fatigue. —Dani Blum and Denise Grady

    Where do college students fall on the list for getting the vaccine? How safe is it to live on college campuses?

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    College students who have no underlying medical conditions are likely to be vaccinated with the general population of healthy adults. Depending on how quickly states can resolve vaccine supply and distribution issues, college students could start getting vaccinated as early as this spring or in the summer.

    Whether students should return to in-person learning on campus depends on the policies of the college they are attending and their own personal risk factors and concerns about Covid-19. This spring many colleges have adopted online-only classes. Other campuses have invited students to live on campus but attend most classes virtually to protect professors, who typically are at higher-risk for complications from Covid. Dickinson College is splitting its semester: First-year students and sophomores are on campus right now; juniors and seniors will switch in halfway through to finish. Some schools have returned to full campus life and tried to impose rules for distancing and large gatherings (some with limited success,) and have been using frequent testing to tamp down outbreaks.

    Tens of thousands of new coronavirus cases continue to emerge on college campuses. A New York Times survey of more than 1,900 American colleges and universities — including every four-year public institution and every private college that competes in N.C.A.A. sports — has revealed more than 397,000 cases and at least 90 deaths since the pandemic began. —Tara Parker-Pope

    Medical Concerns

    Do I need to get the vaccine if I’ve already had Covid-19?

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    Yes. It’s safe, and probably even beneficial, for anyone who has had Covid to get the vaccine at some point, experts said. Although people who have contracted the virus are believed to have at least some natural immunity, it is too soon to know how long it lasts. People who have had Covid in the past are advised to wait about 90 days after infection before getting the shot. —Apoorva Mandavilli

    Will the vaccine work on older adults?

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    All the evidence we have so far suggests that the answer is yes. The clinical trials for the two leading vaccines have shown that they work about the same in older people as younger people. As the vaccines get distributed, the vaccine makers and the C.D.C. will continue to monitor the effectiveness of the vaccine in people 65 and older who, because of age-related changes in their immune systems, often don’t respond as well to vaccination as younger people do. But just as certain flu vaccines have been developed to evoke a stronger immune response in older people, it’s possible that one of the new vaccines could emerge as a better option for this age group. It’s just far too soon to know. —Carl Zimmer

    Were cancer patients studied in the vaccine trials? How does a cancer patient safely get the vaccine?

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    Many cancer patients are struggling to navigate the bumpy rollout of the Covid-19 vaccination campaign. The bottom line is that patients in active treatment should consult with their medical team about how and when to get the vaccine. Some patients may be advised to time the vaccine, if possible, between rounds of chemo — when their white blood cell counts are highest — to optimize their immune response. Ideally, cancer patients in active treatment should receive vaccinations under the care of a doctor, or in a cancer center, where they can be closely monitored and are likely to encounter fewer people than they would at a mass distribution site. The state-by-state nature of vaccination rules can complicate vaccination for cancer patients. For instance, if you live in one state and get cancer treatment in another, your cancer center may not be allowed to give the vaccine to an out-of-state patient.

    According to the American Cancer Society, initial studies testing the Covid-19 vaccines did not include people undergoing chemotherapy or other treatments that suppress the immune system. Of the people included in the Pfizer-BioNTech vaccine trials, 3.7 percent had a history of malignancy at the time of reporting, but it’s believed they were patients in remission or fully recovered, and not patients under active treatment. As a result, it’s not clear how cancer patients in active treatment will respond to the vaccine. In general, most doctors agree that immune-compromised patients will gain some protection from the vaccine, but their bodies may not produce as robust an immune response as a healthy person’s would. —Dani Blum

    I have an autoimmune disease. Will the vaccine work for me?

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    Although people with autoimmune conditions were allowed to enroll in the Covid vaccine trials, patients were excluded if they were taking the type of immune-suppressing drugs used to treat autoimmune disorders. As a result, doctors believe the vaccine is safe for people with autoimmune conditions, but they don’t have specific data showing how well the vaccine will work in these patients.

    Autoimmune conditions such as rheumatoid arthritis or lupus occur when the immune system mistakenly attacks normal body tissues. Treatments that suppress the immune system in an effort to thwart the damage to normal tissues may leave patients more susceptible to infections. In general, doctors have not observed a greatly increased risk of severe Covid-19 infections or death in those with autoimmune disorders, but that may be because people with these conditions are more likely to adhere to strict safety precautions.

    Dr. Alfred Kim, an assistant professor at the Washington University in St. Louis School of Medicine and co-director of the Washington University Lupus Clinic, is currently studying responses to Covid-19 vaccines in people with autoimmune diseases. The study has enrolled about 100 patients so far, with plans to enroll about 500. Dr. Kim said he expects to submit preliminary results to a peer-reviewed journal soon.

    “We anticipate that the safety is going to be no different in people with autoimmune diseases taking immunosuppressants than in people who are not taking any medicines,” Dr. Kim said.

    While it’s possible that people being treated for an autoimmune condition will not generate an immune response to the vaccine that is as powerful as those with a normal immune system, most experts believe the vaccine will offer at least some protection. Dr. Kim said he is hopeful, but wants to wait for the final data.

    “We don’t think there’s going to be a blunting of the vaccine response so great that it’s not going to afford a protective effect from the vaccine,” said Dr. Kim. “That’s what I think the data’s going to look like. But I reserve the right to change my answer six months from now.”

    Even before Covid, people with autoimmune conditions were advised to be more careful about their health, and that should continue after vaccination.

    “You can’t get your vaccine and go hang out at the bars,” said Dr. Helen Talbot, an infectious-disease specialist at Vanderbilt University. “Those with autoimmune diseases will need to continue to be careful well after that.” —Dani Blum

    If I have the virus but don’t know it, will the vaccine still work?

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    While there’s not yet a lot of data about this scenario, vaccine researchers say there’s no cause for additional worry if you find out you were infected at the time of vaccination. “You won’t feel very well, but that’s due to the Covid, not the Covid vaccine,” said Dr. Helen Talbot, a member of a panel advising the Centers for Disease Control and Prevention and an infectious disease specialist at Vanderbilt University.

    It’s unlikely the first dose of vaccine has had enough time to help your body fight the infection, but the vaccine should still spur your body to produce a lasting immune response. Once you’ve recovered, you should plan to get your second dose as planned. “If you unknowingly have the virus and are immunized, the vaccine will not prevent disease but will likely help in the overall development of immune response,” said Dr. Talbot. “You would then get your second immunization once fully recovered — likely after the usual 21 or 28 days. No need to start the vaccine series over." —Dani Blum

    Will it be safe for people with Guillain-Barré Syndrome?

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    Guillain-Barré syndrome is a rare and serious condition that occurs when the body’s immune system attacks the nerves, causing muscle weakness and sometimes paralysis. Nobody knows exactly what causes it, but most patients report that they had recently recovered from a respiratory or gastrointestinal infection. Guillain-Barré syndrome also has been pinpointed as a possible complication of Covid-19.

    According to the Centers for Disease Control and Prevention , there have been no reported cases of anyone developing Guillain-Barré after getting the vaccine for Covid-19 in the early days of the vaccine rollout. In the past, the flu vaccine has been associated with a miniscule risk of Guillain-Barré. In 1976, widespread vaccination against swine flu was associated with a slight increase in Guillain-Barré, estimated at roughly one additional case for every 100,000 people who received the swine flu vaccine. The risk of the seasonal flu shot is much lower, and has consistently been in the range of one to two additional cases of Guillain-Barré per million flu vaccine doses administered.

    There have not been any cases of Guillain-Barré during clinical trials of the Pfizer and Moderna vaccines for Covid-19, but the numbers in the clinical trials and the current vaccination push are still too small to detect such a rare event. “We believe it to be safe, but we won’t know until it’s introduced into millions and millions of people,” said Dr. Helen Talbot, an infectious-disease specialist at Vanderbilt University.

    For people who have had Guillain-Barré in the past, the guidance has been confusing. The official guidance from the Centers for Disease Control and Prevention is that people with a past history of Guillain-Barré should get the Covid vaccine. But Dr. Anthony S. Fauci, the nation’s leading infectious disease expert, has said that he does not recommend that people with a history of Guillain-Barré get the vaccine. “We recommend those people do not get vaccinated because you might trigger a similar serious response,” Dr. Fauci said.

    But not everybody agrees with that advice. Members of the GBS/CIDP International Foundation, an advocacy group for people with Guillain-Barré, wrote an open letter to Dr. Fauci urging people with the syndrome to still get the vaccine. “At this time, there is no reason that those who had GBS in the past cannot get the current Covid vaccines,” they wrote. “If they have concerns, they should speak to their local health care professionals.” —Dani Blum

    Were transplant recipients included in the studies? Is it safe for us to get vaccinated?

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    Transplant patients were not included in the vaccine trials. Despite the lack of information, transplant advocacy groups have urged patients to get the Pfizer or Moderna vaccines. Transplant patients, who must take drugs that suppress their immune systems, are at high risk for complications if they contract Covid-19. Research shows transplant patients with Covid-19 have a 30 percent increased risk of dying than patients with no underlying risk factors. Although the vaccine hasn’t been studied in transplant patients, doctors know that vaccines that do not involve giving a transplant patient a living virus are generally safe. The Pfizer and Moderna vaccines use messenger RNA molecules to stimulate the immune system and do not contain any form of live, dead or neutralized virus. The American Society of Transplantation created a fact sheet for transplant patients, and advises patients who get vaccinated to continue to wear a mask and take precautions to avoid being exposed to the coronavirus. A team at Johns Hopkins Medicine has initiated an observational study of transplant recipients who get the vaccine. Preliminary information from the study should be available around February. —Tara Parker-Pope

    Do we know if these vaccines will be safe for people with H.I.V.?

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    Trials studying the Covid-19 vaccine have included people with H.I.V., albeit in small numbers. The Pfizer trial included 120 people with H.I.V., and the Moderna trial included 176 people with H.I.V., according to Poz , a news site for people living with and those affected by H.I.V./AIDS. Although the numbers are too small to draw meaningful conclusions, no unusual safety concerns were reported for people with H.I.V. Because the Pfizer and Moderna vaccines do not contain weakened or inactivated virus, they are believed to be a safe option for people with H.I.V. and AIDS. The Centers for Disease Control said people with H.I.V. “should be counseled” about the unknowns, including safety and effectiveness in “immunocompromised populations.” People with compromised immune systems may not produce a robust immune response to the vaccine, and should continue to follow all current guidance to protect themselves against Covid-19, the C.D.C. said. —Tara Parker-Pope

    Understanding the Vaccine

    Are there new vaccines coming soon?

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    There are about a dozen vaccines approved for use around the world. In the U.S., vaccines from Pfizer-BioNTech, Moderna and Johnson & Johnson have received emergency use authorization. A fourth vaccine, from the Maryland-based company Novavax, could apply for emergency use authorization in late April. The Novavax vaccine requires two doses, three weeks apart. The government has already ordered 110 million doses of the Novavax vaccine, to be delivered by the end of June, and Novavax has said it believes it can meet that target. Tens of millions of doses of another vaccine from AstraZeneca have been sitting in American manufacturing sites. While their use has already been approved in dozens of countries, including Mexico and Canada, the vaccine has not yet been authorized by American regulators. In March, President Biden said the United States was planning to share 2.5 million doses of the vaccine with Mexico and 1.5 million with Canada. —Carl Zimmer

    How do these new genetic vaccines work?

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    Although these are described as “genetic” vaccines, the new Covid vaccines don’t alter your genes in any way. Instead, the Pfizer-BioNTech and Moderna vaccines use a genetic molecule to prime the immune system. That molecule is known as mRNA — the “m” stands for messenger. Think of this molecule like a set of instructions. While a traditional vaccine uses a weakened or inactivated germ to trigger an immune response in our bodies, the mRNA vaccines carry a set of instructions to teach our cells how to make a protein that will trigger an immune response and produce antibodies to the virus.

    Here’s how it works. When you get your shot in the arm, the injection includes the messenger molecule, which is packaged in an oily bubble that fuses to a cell. The cell then uses the mRNA molecule as a set of instructions to make something called a “spike protein.” (The surface of the coronavirus is covered with similar spikes.)

    Your immune system quickly recognizes that the spike protein is a foreign invader, and begins attacking it. The vaccine has essentially trained your immune system to recognize and attack the spike. Now, if you ever come into contact with the actual coronavirus, your immune system has learned how to handle it. You can learn more about mRNA vaccines from the Centers for Disease Control and Prevention website. —Tara Parker-Pope

    Does the mRNA molecule in the new vaccines alter my genes?

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    No! The messenger RNA used in the in the Pfizer and Moderna vaccines never enters the nucleus of your cells and has no effect on your DNA. The mRNA molecule survives long enough for your cells to copy the instructions and create the spike protein that is used to train your immune system against coronavirus. So what happens to the molecule after it delivers these instructions? It lasts a few days, and then the cell shreds it and gets rid of it using special enzymes. It’s important to understand that the vaccine mimics a natural process that goes on in your body every day. At any moment, each of our cells may contain hundreds of thousands of mRNA molecules, which they produce in order to make a wide variety of proteins of their own. —Tara Parker-Pope and Carl Zimmer

    How does the Johnson & Johnson vaccine work compared to the Pfizer and Moderna vaccines?

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    Like the Pfizer and Moderna vaccines, the Johnson & Johnson vaccine gives the body a set of instructions to build a spike protein that can train the immune system to ward off a coronavirus infection. While the Pfizer and Moderna vaccines use a genetic molecule called mRNA to provide the instructions, the Johnson & Johnson vaccine uses DNA to give the message, and the DNA is carried by a so-called viral vector, Adenovirus 26. Adenoviruses are common viruses that typically cause colds or flu-like symptoms. The Johnson & Johnson team used a modified adenovirus that can enter cells to deliver the instructions, but can’t replicate inside them or cause illness.

    Johnson & Johnson’s vaccine comes out of decades of research on adenovirus-based vaccines. In July, the first one was approved for general use — a vaccine for Ebola, also made by Johnson & Johnson. The company is also running trials on adenovirus-based vaccines for other diseases, including H.I.V. and Zika. Some other coronavirus vaccines are also based on adenoviruses, such as the one developed by the University of Oxford and AstraZeneca, using a chimpanzee adenovirus.

    Adenovirus-based vaccines for Covid-19 are more rugged than mRNA vaccines from Pfizer and Moderna. DNA is not as fragile as RNA, and the adenovirus’s tough protein coat helps protect the genetic material inside. As a result, the Johnson & Johnson vaccine can be stored using traditional refrigeration methods for up to three months. —Carl Zimmer and Tara Parker-Pope

    What is the status of the AstraZeneca vaccine in the United States?

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    While more than 70 countries have authorized the vaccine, the United States has not. AstraZeneca has not yet applied to the Food and Drug Administration for authorization and is waiting for results from its U.S. trial that enrolled more than 32,000 participants. An announcement from AstraZeneca about those results could come soon. —Denise Grady and Rebecca Robbins

    Why not take my chances with Covid-19 rather than get a vaccine?

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    Covid-19 is by far the more dangerous option. Covid vaccines carry little known risk. But the perils of Covid-19 have been well documented. About 20 percent of people who come down with Covid-19 symptoms develop serious, potentially life-threatening illness. Although people who are older, obese or have other health problems are at highest risk for complications from Covid-19, younger people can become severely ill, too. In a study of more than 3,000 people ages 18 to 34 who were hospitalized for Covid, 20 percent required intensive care and 3 percent died.

    The long-term health complications associated with Covid-19 are a serious concern. As many as one in three people who recover from Covid have chronic complaints for months afterward, including exhaustion, a racing heart, blood clots and loss of sense of smell or taste. —Apoorva Mandavilli

    Will the vaccines work against the new variants that have emerged around the world?

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    Moderna and Pfizer-BioNTech both said their vaccines were effective against new variants of the coronavirus discovered in Britain and South Africa. But they are slightly less protective against the variant in South Africa, which may be more adept at dodging antibodies in the bloodstream. A third vaccine candidate, Novavax, is about 90 percent effective against the original strain of coronavirus, but only about 50 percent effective against the variant in South Africa. While that sounds like bad news, it was reassuring that the variant could not entirely evade the vaccine. Company officials believe they can adjust the vaccine to improve its effectiveness against the variant.

    Researchers at Moderna examined blood samples from eight people who had received two doses of the vaccine, and two monkeys that had been immunized. Neutralizing antibodies — the type that can disable the virus — were just as effective against the variant identified in Britain as they were against the original form of the virus. But with the variant circulating in South Africa, there was a sixfold reduction in the antibodies’ effectiveness. Even so, the company said, those antibodies “remain above levels that are expected to be protective.”

    As a precaution, Moderna has begun developing a new form of its vaccine that could be used as a booster shot against the variant in South Africa. Moderna said it also planned to begin testing whether giving patients a third shot of its original vaccine as a booster could help fend off newly emerging forms of the virus. BioNTech could develop a newly adjusted vaccine against the variants in about six weeks, he said. The Food and Drug Administration has not commented on what its policy will be for authorizing vaccines that have been updated to work better against new variants.

    Scientists had predicted that the coronavirus would evolve and might acquire new mutations that would thwart vaccines, but few researchers expected it to happen so soon. A big part of the problem is that the virus has spread unchecked in many parts of the world. Each new infection gives the coronavirus more chances to mutate, creating new variants. —Denise Grady, Apoorva Mandavilli and Katie Thomas

    If the vaccines need to stay frozen, how are they transported and delivered?

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    Planning for the transportation and distribution of the vaccines has been in the works for months. Although the Covid vaccines are new, pharmacies and transportation companies have a great deal of experience distributing vaccines and putting shots in people’s arms. But the first two Covid vaccines, from Pfizer and Moderna, present a unique challenge because they must be kept in freezing conditions.

    UPS and FedEx already have networks of freezers that they use to ship perishable food and medical supplies. The companies also have experience shipping vaccines for other illnesses, including the seasonal flu. UPS has constructed a so-called freezer farm in Louisville, Ky., the company’s largest hub, where it can store millions of doses at subzero temperatures. FedEx said that it beefed up its cold-chain infrastructure during the H1N1 pandemic in 2019, and has added more freezers and refrigerated trailers to prepare for Covid vaccine distribution. FedEx and UPS are transporting the vaccine throughout most of the country, and each delivery is followed by shipments of extra dry ice a day later. Pfizer designed special containers, with trackers and enough dry ice to keep the doses sufficiently cold for up to 10 days.

    Every truck carrying the containers will have a device that tracks its location, temperature, light exposure and motion. And vaccine makers and the federal government have been working with hospitals, pharmacies and other vaccination sites to make sure they are equipped with adequate freezers, special containers and supplies of dry ice to store the vaccines. —Abby Goodnough and David Gelles

    I’ve heard rumors and jokes about microchips in the new vaccines. What is that about?

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    The false conspiracy theory about microchips emerged after Bill Gates, the founder of Microsoft, made a comment about “digital certificates” that might one day be used to show a person had been tested or vaccinated for Covid-19. The reference prompted conspiracy theories to circulate online speculating that a tracking microchip would be planted by the government to surveil the movements of Americans. For months, widely shared videos and viral posts on social media have baselessly claimed that such technologies could find their way into syringes delivering shots. None of the rumors are true.

    The Pfizer and Moderna vaccines have one active ingredient: a molecule called messenger RNA, or mRNA, which contains genetic instructions for a coronavirus protein called spike. Once injected, the mRNA will instruct human cells to manufacture spike, exposing the immune system to a highly recognizable feature of the virus. The remaining ingredients are lipids, including cholesterol, that form a fatty bubble around the fragile mRNA molecule, as well as sucrose (sugar) and various salts. —Katherine J. Wu and Tara Parker-Pope

    What is the difference between emergency use authorization vs. normal approval of a vaccine?

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    An emergency use authorization, like the one given to the Pfizer and Moderna vaccines, is surprisingly similar to a standard approval. It includes the same basic steps — preclinical testing, Phase 1 safety trials, Phase 2 expanded trials and Phase 3 efficacy trials — that would be required in the traditional approval process. The main difference is that, in an emergency, the Food and Drug Administration gives the application priority and speeds up its own review of the research. One way to do that is to solve logistical concerns early, while waiting for clinical trials to finish. For instance, the F.D.A. worked with the vaccine companies to solve manufacturing and distribution issues before the firms had completed their clinical trials or submitted applications for emergency use. In an interview with Scientific American magazine, the former F.D.A. commissioner Dr. Stephen Hahn said that in an emergency, the agency can prioritize an application over other demands to reduce the four-to-six-month review process to just several weeks.

    Once vaccine makers win an emergency use authorization, they are expected to continue collecting information on the safety and efficacy of the vaccine and apply for a license, which is the final step in the approval process. Additional data will be collected on special patient populations like children, pregnant women and immune-compromised patients who weren’t studied in the first round of research. —Tara Parker-Pope and Carl Zimmer

    What about the billions of people who live outside the United States? How will the rest of the planet get vaccinated?

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    Vaccination efforts against Covid-19 have revealed an extraordinary gap in access to the vaccines around the world. Rich nations like the United States and Britain have cut deals with multiple drug manufacturers and secured enough doses of vaccines likely to come on the market this year to immunize their citizens multiple times over. China and Russia have developed their own vaccines and begun mass immunization programs. In stark contrast, most poor nations rely on a complex global vaccine-sharing initiative called Covax, and are likely to receive only enough doses to vaccinate at most 25 percent of their populations this year. Run by the World Health Organization and two global nonprofits, Covax relies on financial assistance and other support from wealthy nations. It wasn’t until this month that the U.S. agreed to participate and provide funding.

    Some less wealthy nations have their own local vaccine-manufacturing capacity and have leveraged it. India is on track to produce more doses of Covid-19 vaccines next year than any other country. The Serum Institute of India, which has contracts for large quantities of the AstraZeneca and Novavax vaccines, has promised the Indian government half of its output. And the billionaire Carlos Slim has helped fund a deal for 150 million doses of the AstraZeneca vaccine in Latin America, drawing on manufacturing capacities in Argentina and his native Mexico.

    China, which has the third-biggest vaccine-manufacturing capacity in the world, has indicated that it intends to make its vaccines available to poor countries. But the outlook for most of the developing world is dire. Because of manufacturing limits, it could take until 2024 for many low-income countries to obtain enough vaccines to fully immunize their populations. —Megan Twohey, Keith Collins and Katie Thomas

    After Vaccination

    How long will the vaccine last? Will I need another one next year?

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    That is to be determined. It’s possible that Covid-19 vaccinations will become an annual event, just like the flu shot. Or it may be that the benefits of the vaccine last longer than a year. We have to wait to see how durable the protection from the vaccines is. To determine this, researchers are going to be tracking vaccinated people to look for “breakthrough cases” — those people who get sick with Covid-19 despite vaccination. That is a sign of weakening protection and will give researchers clues about how long the vaccine lasts. They will also be monitoring levels of antibodies and T cells in the blood of vaccinated people to determine whether and when a booster shot might be needed. It’s conceivable that people may need boosters every few months, once a year or only every few years. It’s just a matter of waiting for the data. —Carl Zimmer

    If I’ve been vaccinated, why do I still need to wear a mask?

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    The answer depends on the circumstances that you find yourself in. Let’s start at the beginning. It takes a while for the vaccine’s protection to kick in — so you’re still vulnerable to catching the coronavirus until about a week or two after getting your second dose, which is why you need to keep wearing your mask in the early weeks after vaccination.

    Once you’re fully vaccinated, you’ll still need to wear a mask in public spaces. Federal, state and city mask mandates will remain in place for a while. Even though you got the shot, millions more people remain unprotected — and there’s no way to easily discern who has been vaccinated and who hasn’t. There’s also a theoretical concern that a vaccinated person might carry the virus in their nose and not get sick, but still sneeze or breathe it onto other people. Based on studies of flu vaccine and even patients who are sick with Covid-19, researchers have reason to be hopeful that vaccinated people won’t spread the virus, but more research is needed. So until everyone is vaccinated, it’s best to wear a mask around other people. —Tara Parker-Pope

    If I’m vaccinated, and all my friends and family are vaccinated, can we hang out together without masks?

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    In short, yes, although there are still some precautions you’ll want to consider before removing your mask. I asked Dr. Ashish K. Jha, dean of the Brown University School of Public Health, for guidance. He says there are four questions to ask if you want to spend time indoors with other vaccinated people, without masks.

    - Are you vaccinated?

    - Is everyone else in the room vaccinated?

    - What’s the level of spread in the community?

    - Is someone in the room at high risk?

    Even if everyone in the room is vaccinated, you need to think about the last two questions. The vaccine gives you about 95 percent protection (an estimate based on data from tightly controlled clinical trials — not the real world). But you also need to think about your odds of coming into contact with the virus. A 5 percent risk of infection when the virus is raging is still a significant risk.

    “If the risk of infection is very, very bad, then 95 percent is not low enough while the case loads are as high as they are in the U.S.,” Dr. Jha said. “People should probably be wearing a mask even after vaccination. Over time as infection numbers come way down, let’s say you have a 5 percent risk off a low baseline — then it becomes much safer.”

    The final question — is someone in the room at high risk — is also important. Even if a high-risk person is vaccinated, you need to take extra precautions when virus case counts are high in your community. And you have to factor in the fact that the vaccine may not be 95 percent effective in every single person — an older person or someone with a less efficient immune system might get less protection from the vaccine than a young, healthy person.

    “In a raging pandemic and things are horrible, and I visit my elderly parents, and I’ve been vaccinated — I’m still going to be careful; my risk tolerance is low,” Dr. Jha said. “I’m going to have a different threshold with my 82-year-old dad than with my 47-year-old friend. As the pandemic gets better, I think we are going to be able to relax more.”

    Unfortunately, a lot of the public health messaging around the vaccine has been to remind people to keep wearing masks rather than also reminding them that after vaccination and with the right precautions, we will be able to safely socialize with other vaccinated people, without having to wear a mask. —Tara Parker-Pope

    Will my employer require vaccinations?

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    Employers do have the right to compel their workers to be vaccinated once a vaccine is formally approved. Many hospital systems, for example, require annual flu shots. But employees can seek exemptions based on medical reasons or religious beliefs. In such cases, employers are supposed to provide a “reasonable accommodation” — with a coronavirus vaccine, for example, a worker might be allowed to work if they wear a mask, or to work from home. —Abby Goodnough

    Will I be required to provide proof of vaccination to travel?

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    Currently there are no proof-of-vaccination requirements to travel, but that may change in the future. For now the focus is on providing proof that you have tested negative for the virus. All international passengers (including U.S. citizens) headed to the United States will first need to show proof of a negative coronavirus test before boarding their flights, according to a new federal policy going into effect on Jan. 26.

    The new policy requires all air passengers, regardless of vaccination status, to get a test for current infection within the three days before a scheduled flight to the United States, and to provide written documentation of their test results or proof of having recovered from Covid-19. Proof of immunization will not be sufficient, because vaccinated people may still become infected, in theory, and transmit the virus on a flight, said a spokesman for the Centers for Disease Control and Prevention.

    Major airlines including United, JetBlue and Lufthansa plan to use a health passport app, called CommonPass, that can verify passengers’ coronavirus test results and vaccination status. CommonPass notifies users of local travel rules — like having to provide proof of a negative virus test — and then aims to check that they have met them. The company’s website says the app will be available soon in the Apple app store and on Google Play. —Natasha Singer and Apoorva Mandavilli

    How will we know how well the vaccines are working?

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    An individual won’t know their personal level of protection after being vaccinated, but in the months after shots are put into people’s arms, a number of studies will continue to monitor how well the vaccines work across the population. The main goal will be to study rates of Covid-19 in groups of people who are vaccinated compared with rates in those who did not receive the vaccine. (Safety studies will also continue to determine whether any additional side effects or serious health risks occur after vaccination.)

    “You’ll be able to look retrospectively at what the effectiveness is,” said Dr. Paul A. Offit, a professor at the University of Pennsylvania and a member of the Food and Drug Administration’s vaccine advisory panel. Clinical trials “show efficacy in controlled conditions, but you’ll be able to see the effectiveness of the vaccines in the real world,” he added.

    A number of factors can change how a vaccine performs in the real world: how it’s stored, whether proper vaccination procedures are followed and the types of patients getting the vaccine, including those with underlying medical conditions who weren’t studied in the original trials. To see how the vaccines are doing, federal health officials, company researchers and academic experts will be tracking large groups of people, collecting data from medical records and monitoring people in nursing homes and the military. Experts will study racial and ethnic minority groups as well as specific patient groups like those with heart conditions, obesity, or autoimmune conditions to see how well they are protected from Covid-19. You can read more about efforts by the Centers for Disease Control and Prevention to ensure the vaccines work. —Dani Blum and Tara Parker-Pope

    How will we know when things are getting better?

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    When case counts start dropping and the test positivity rate in every state drops below 5 percent, we’ll know things are looking up. The test positivity rate is the percentage of overall tests given in a community that come back positive. The lower the number, the fewer new cases and the less likely you are to cross paths with someone who has the virus. In some states the test positivity rate is 20 or 30 percent — showing the virus is raging out of control. In other states, like Vermont, Connecticut and Hawaii, compliance with public health measures has been keeping the positivity rate below 3 percent, meaning the risk of catching the virus in those states is much lower than in other parts of the country. Ideally, once 70 percent to 85 percent of the country is vaccinated, the test positivity rate in every state will drop well below 5 percent. “The best number is zero,” Dr. Anthony S. Fauci said. “It’s never going to be zero, but anywhere close to that is great.” —Tara Parker-Pope

    When will it be safe to do things like going to the movies or the theater again?

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    Public health officials estimate that between 70 to 85 percent of the population needs to be vaccinated before people can start moving freely again in society. If things go well, life could get a lot better by late spring and early summer. “It depends on the uptake of the vaccine and the level of infection in the community,” Dr. Fauci said. “If it turns out that only 50 percent get vaccinated, then it’s going to take much, much longer to get back to the kind of normality that we’d like to see." —Tara Parker-Pope

    What are the odds we’ll get to 70 to 85 percent vaccination rates any time soon?

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    Despite recent bottlenecks that have slowed distribution of the vaccine, most health experts are optimistic that by this spring most supply issues will be solved, and we will have gotten better at widespread vaccination. The rest will depend on the public’s willingness to get the vaccine. While vaccine hesitancy remains a concern, there are signs that confidence in the vaccine is rising in the United States and around the world.

    In June, a global survey of 13,426 people in 19 countries found that 71.5 percent said they would be very likely or somewhat likely to take the Covid-19 vaccine. Differences in acceptance rates ranged from almost 90 percent of those surveyed in China to less than 55 percent in Russia.

    In the United States, the Kaiser Family Foundation has begun issuing a regular report called the KFF Covid-19 Vaccine Monitor, which tracks the public’s view of the vaccines. The KFF survey in December showed 71 percent of people said they would definitely or probably get a vaccine for Covid-19, “if it was determined to be safe by scientists and available for free to everyone who wanted it.” That’s an increase from the 63 percent who responded the same way in the foundation’s September survey. The gains in confidence were seen across racial and ethnic groups, and among both Democrats and Republicans.

    About 27 percent of the public remains vaccine hesitant, the survey found. Vaccine hesitancy is highest among Republicans (42 percent), those ages 30-49 (36 percent), and rural residents (35 percent). There are some troubling trends in the survey data. Among people who work in a health care setting, 29 percent are vaccine hesitant, as are 33 percent of those in the “essential worker” category. Also concerning, 35 percent of Black adults , who have suffered higher rates of infection and mortality during the pandemic, say they definitely or probably would not get vaccinated. —Tara Parker-Pope

    If you still have questions after reading this guide, tell us what else you want to know using this form.

    Design and production by Rebecca Lieberman and Jaspal Riyait. Additional production by Dani Blum, Tara Parker-Pope and Karen Barrow.

    Illustration by Timo Lenzen.

    Research & Development contributions by Jack Cook and Amelia Pisapia.

    Reporting was contributed by Tara Parker-Pope, Dani Blum, Keith Collins, David Gelles, Abby Goodnough, Amy Harmon, Dana Goldstein, Denise Grady, Sarah Kliff, Sharon LaFraniere, Apoorva Mandavilli, Donald G. McNeil Jr., Amelia Nierenberg, Adam Pasick, Natasha Singer, Sheryl Gay Stolberg, Katie Thomas, Lucy Tompkins, Megan Twohey, Carl Zimmer, Noah Weilan and Katherine J. Wu.