Your Latest Covid Questions, Answered

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When the Covid-19 pandemic began, we had a seemingly endless amount of questions and few answers. Now, nearly three years later, we’re still learning how to live with the virus. We have been confronted with multiple subvariants and new symptoms, and we have vaccines to protect us from severe illness. Still, while many questions remain unanswered, there’s a lot we have learned about the virus and how to navigate our lives in its midst.

Here are answers to some of the latest Covid questions:

Contributors: Pam Belluck, Dani Blum, Apoorva Mandavilli, Melinda Wenner Moyer, Sharon Otterman, Tara Parker-Pope, Knvul Sheikh, Nicole Stock

What are the symptoms of an infection with BQ.1 and BQ.1.1?

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Two new iterations of the Omicron variant have found their way to the top of the list of Covid subvariants circulating in the U.S. BQ.1.1 and BQ.1 now together account for nearly 70 percent of cases in the U.S., according to the Centers for Disease Control and Prevention — squeezing out BA.5, which was dominant over the summer.

BA.5 is characterized by relatively mild cold and flu-like symptoms, with many people complaining about sore throats. BQ.1.1 and BQ.1 do not have radically different symptoms from previous versions of Omicron in vaccinated people, said Dr. Steven Gordon, an infectious disease specialist at the Cleveland Clinic. People infected with these subvariants also tend to report cold symptoms: sore throats, runny noses, muscle aches, coughs and headaches. Symptoms are typically more prolonged in unvaccinated people, compared with those who are vaccinated, said Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco. Fever is much more common in people who are unvaccinated, he added.

If you have an unexplained sore throat, and then develop a fever and night sweats, “it’s much more likely to be Covid than your run of the mill cold,” said Dr. Justin Fiala, a pulmonary and critical care specialist at Northwestern Medicine. BQ.1.1 and BQ.1 symptoms are more or less centered around and above the throat, Dr. Fiala said, as opposed to earlier versions of the virus, which affected the lungs.

How do I know if my symptoms are from Covid, the common cold, flu or R.S.V.?

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The flu, Covid and respiratory syncytial virus (R.S.V.) have symptoms that overlap — and also can look quite similar to those of the common cold, which is caused by a variety of viruses. You can develop a cough, fever, headache or runny or stuffy nose with any respiratory virus, said Dr. Michael Chang, an infectious disease specialist at Memorial Hermann Health System in Houston.

One way to differentiate among viral infections is to monitor how quickly your symptoms ramp up. Symptoms of the flu come on quickly — often just one day after exposure to someone who was sick — and can be felt all over the body. People with the flu often describe feeling like they’ve been hit by a truck, Dr. Chang said. With colds, symptoms may take two or three days to appear and are much milder.

Covid and R.S.V. have even longer incubation periods. It can take an average of five days from exposure to the coronavirus to the development of early Covid-19 symptoms, though newer subvariants like BQ.1 and BQ.1.1 may result in an active infection as soon as three days after exposure. R.S.V. takes about four to six days. With Covid and R.S.V., symptoms also build slowly: You may start out feeling sniffly, then develop a cough or a headache the next day and a fever the next.

Adults afflicted with the flu are likely to experience very high fevers, up to 103 or 104 degrees, Dr. Chang said. But fevers rarely accompany colds, particularly in adults. People with Covid-19 and R.S.V. experience mild fevers or none at all. “Especially with the newer variants and people having been exposed through immunization or if they’ve had an infection before, we’re seeing that more patients are now only mildly symptomatic, and they only have low-grade fevers, around 99 or 100,” Dr. Chang said.

A few symptoms are unique to Covid, such as brain fog, which occurs most frequently in older adults. Some people with Covid lose their sense of taste and smell, while others occasionally experience rashes and blisters on their toes or a sudden onset of hair loss.

People with R.S.V. are unlikely to feel muscle aches and fatigue. Instead, R.S.V. is often accompanied by a distinctive wet and forceful cough. Young children with R.S.V. may also produce a high-pitched wheezing sound when they exhale.

Compared to adults, young children experience more severe symptoms of R.S.V. and the flu — but kids seem to have more asymptomatic or mild bouts of Covid-19. People over the age of 65, those with underlying medical conditions and pregnant women can experience severe illness with all three viruses.

The only reliable way to tell which infection you have is by testing, said Dr. Adam Ratner, a pediatric infectious disease specialist at N.Y.U. Langone. An at-home Covid test can quickly determine whether or not you have the virus, although testing too soon after infection can lead to false negatives. Experts advise taking a second rapid test 24 to 48 hours after the first, to ensure the results are accurate.

You can also try a combined P.C.R. test developed by Labcorp that allows you to take a nasal swab for Covid-19, flu and R.S.V. and mail the sample to a lab. Results take one or two days. Most clinics, urgent care centers and hospitals also offer combination tests for all three viruses.

We’ve also created this interactive guide to help — you can mark symptoms and then sort by selecting an illness below.

Rarely

•• Sometimes

••• Often

*A stuffy nose may temporarily decrease the ability to taste or smell but it does not cause a sudden, complete loss of these senses.

Source: Centers for Disease Control and Prevention

I tested positive. Now what?

If you’re around other people when you get the bad news, the first thing you should do is put on a mask. Then, isolate yourself as quickly as possible, even if you don’t have symptoms and even if you are vaccinated.

Once you take a deep breath and have a moment, think about where you’ve been and who might have inhaled your germs. Then, let your employer know. Many workplaces have protocols for contact tracing when an employee tests positive. You should also alert anyone with whom you’ve spent time, going back at least two days before you got tested or started having symptoms, said Dr. Paul Sax, an infectious disease expert at Brigham and Women’s Hospital and a professor at Harvard Medical School. The C.D.C. defines a close contact as anyone who was less than six feet from you for 15 minutes or more.

Don’t forget to also tell your doctor, if you have one, particularly if you have an underlying medical condition, like high blood pressure or diabetes, that puts you at higher risk.

If your child tests positive, call the pediatrician. You also need to call your child’s school as well as anyone with whom your child has had close contact with at play dates, parties or other activities.

Dani Blum and

What am I allowed to do after Day 5 of a Covid infection?

A woman, clad in a white face mask and a white button-down shirt, pushing a cart of groceries.
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A year ago this month, the Centers for Disease Control and Prevention updated and shortened its guidelines for how long to isolate if you test positive for Covid, making Day 5 a critical juncture. It is the point after which, under certain circumstances, you can leave your home. Antiviral medications, like Paxlovid, are also most effective if taken by Day 5, and they can reduce severe symptoms and significantly lower the risk of hospitalization and death. But Day 5 isn’t the end of the road for everyone. Some Covid patients continue to test positive or to feel sick beyond that point. Here’s what to know about the timeline.

If you have not developed any symptoms during your Covid infection, the C.D.C. says, you can stop isolating after Day 5. For counting purposes, the first day you feel any symptoms is considered Day 0; Day 1 is the first full day after. Those without symptoms can count Day 0 as the day they were tested.

For those who have symptoms, the severity matters: If you experienced difficulty breathing during your illness, you must continue isolating through Day 10. If your symptoms are mild and improving — for example, you have less of a cough or your congestion is clearing up — you can stop isolating after Day 5, the C.D.C. says, but with some precautions: You must remain fever-free without medication for 24 hours, and you need to wear a high-quality mask indoors any time you’re around other people through Day 10.

Some people think, mistakenly, that the C.D.C. guidance means you can go straight back to normal after Day 5, said Dr. Mark Mulligan, an infectious disease specialist at NYU Langone. If your symptoms are better on Day 6, you can go to the grocery store in a KN95, for example, but you shouldn’t eat in an indoor restaurant or stop by a neighbor’s house unmasked.

That said, you can go about your life without a mask if your symptoms have cleared up and you test negative on two antigen tests 48 hours apart after you leave isolation. Meaning, if you’re feeling better and you test negative on Day 6 and again on Day 8, you’re good to go.

“The best practice, from a scientific standpoint, would be that you don’t go out and interact with people unmasked until you see that you don’t have the virus,” said Dr. Justin Fiala, a pulmonary and critical care specialist at Northwestern Medicine. “As long as that virus is detectable in the nose, assume that it’s exhaled with every single breath.”

It’s not always clear when, exactly, you can expect your symptoms to improve. Earlier in the pandemic, before vaccines were introduced, some people developed an inflammatory response to the virus approximately five days or more after symptoms started. After thinking they were on the mend, they might suddenly struggle to breathe.

Covid now follows a pattern more similar to that of other respiratory viruses, said Dr. Kelly Gebo, an infectious disease specialist at Johns Hopkins Medicine: Most patients generally get better after their initial infection, although the disease can have a more complicated course in people who are older, immunocompromised or have an underlying condition associated with a higher risk of severe disease.

A subset of people will continue to test positive for the virus up until and potentially beyond Day 10, said Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco. (People may test positive for up to 90 days on P.C.R. tests, and some may continue to test positive beyond 10 days on antigen tests.) After Day 5, however, symptoms are usually improving or have receded fully in vaccinated people without underlying health conditions. Some people may have lingering symptoms, like a cough or fatigue, that can persist for up to a month or, in rare cases, longer; if their symptoms are improving, they can leave isolation.

In some cases, people who thought they were better may experience a rebound of their Covid symptoms. This phenomenon was reported by patients who took Paxlovid, but a study in the fall found that more than a third of those who recovered from an infection experienced a return of their symptoms days or weeks later even without the antiviral medication.

If any symptoms persist for longer than four weeks after the initial infection, the C.D.C. could start to classify the patient as having “long Covid.” While people with long Covid typically are not contagious, they may continue to have an erratic heart rate, loss of taste or smell, brain fog, dizziness, depression or other complications, and doctors are researching potential therapies and treatments.

Can I get Covid-19 and the flu at the same time? What about Covid and R.S.V.?

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It is possible to get multiple infections at once. Researchers have found cases of people testing positive for both Covid-19 and the flu since the beginning of the pandemic. While respiratory syncytial virus infections are not as common in adults as they are in children and seniors, it is also possible for someone to have Covid and R.S.V. — or any other viral infection, for that matter.

“But it’s not as common as we thought it might be,” said Dr. Michael Chang, a pediatric infectious disease specialist at Memorial Hermann Health System in Houston.

Social distancing and masking during the first two years of the pandemic may have protected people from getting co-infections with other respiratory viruses, Dr. Chang said. And even as R.S.V. and flu cases are reaching record highs this year, in surges that have been labeled a “tripledemic,” these viruses are not peaking at the same time in the same parts of the country.

“If it feels like everyone you know has been sick since the beginning of September, it’s because we’ve had different viruses peak one right after the other,” said Dr. Dana Mazo, an infectious diseases specialist and clinical associate professor of medicine at NYU Langone Health. “In September, we had a lot of rhinovirus and enterovirus, which cause the common cold. At the beginning of October, we saw R.S.V. surge and then flu is sort of peaking right now.” That pattern has varied in different regions of the country.

If you are unlucky enough to get two respiratory infections at once, that doesn’t necessarily mean you will be doubly sick. Your innate immune system, which serves as the body’s first line of defense, is not particularly discerning against different pathogens. So when you get infected with a virus, the innate immune response is already revved up, and could help the body detect and fight off another pathogen. As a result, the second infection may be slightly less severe, or it may resolve a bit sooner.

But because every person’s immune response varies based on their genetics, the kinds of pathogens they’ve been exposed to before and the types of medications they may be using, scientists don’t yet know for sure if everyone experiences that immune benefit. According to Dr. Chang, there’s just as much a chance that one infection will make you more vulnerable to another pathogen. R.S.V., for example, can increase the risk of secondary bacterial infections, such as ear infections, particularly in young children.

Certain other groups may also be more susceptible to co-infection. Pregnant women, people above 65 and those who are immunocompromised are already at high risk for Covid-19, the flu and R.S.V. They may be even more likely to have severe disease if doubly infected. And data shows that people who are opposed to getting one vaccine also tend to refuse others — a trend that has been accelerating because of Covid vaccine misinformation earlier in the pandemic. People who are not vaccinated for Covid or the flu are at higher risk of getting both viruses, Dr. Chang said.

You may not know you have a co-infection unless you get tested for more than one virus. Respiratory infections often have incredibly similar symptoms. And unless you need treatment in a hospital, doctors said that infection management would be the same regardless of what you infection have: rest at home and recover with plenty of fluids and a few over-the-counter medicines. But if your symptoms are serious, or you have trouble breathing, you should talk to a health care provider and see if you are eligible for antiviral treatment.

The home test is negative, but could I still have Covid?

Credit...Ibrahim Rayintakath

What does a negative result on a home Covid-19 test really mean?

That’s the question that has confounded many people who have reached for a home test because they have a sore throat, cough or runny nose. After swabbing their nose and waiting an anxious 15 minutes, the result is negative.

While there’s relief in getting a negative result, there’s also uncertainty. Am I really free of Covid? Or did the test just not detect it? Should I test again? Can I spend time with other people?

The confusion is justified, say testing and public health experts. It stems from a lack of understanding about how the tests work. Rapid home antigen tests look for pieces of viral proteins from a swab of your nose, and they are designed to identify whether you have an infectious level of the virus. But a negative test is not a guarantee you don’t have Covid.

It could be that your symptoms are an immune response signaling the arrival of Covid or another invader. The harder your immune system is working to tamp down the virus, particularly an immune system supercharged by vaccine antibodies, the more likely you are to get an early negative result on a rapid test, even if you’re infected.

“It may be that the virus in your body is having a tug of war with your immune system,” said Dr. Michael Mina, chief science officer for eMed, a company that helps rapid test users get treatment from home. “If you test negative and you have symptoms, don’t assume you’re negative. Assume that the virus has not had an opportunity to grow up yet. The symptoms might mean your immune system is just triggering a very early warning.”

Dr. Mina advises people to take a rapid test on the first day of symptoms. A positive result means you almost certainly have Covid. If the result is negative and your symptoms continue, you should still take precautions, wear a mask and avoid close contact with other people. If you can’t test daily, then wait 48 hours and test again. If you’re still negative but your symptoms persist or are getting worse, you should take another test on Day 4. Or you may want to go to a testing center to take a P.C.R. test, which can sometimes detect Covid a little sooner than a home test, although you may have to wait a day or two for the results.

Experts say that if you have symptoms and continue to get negative results on home tests, it may be that your immune system is doing a good job beating the virus. Or it could be that you have another illness. Either way, you should try to avoid infecting others.

“If you have symptoms and continue to test negative, the chances that you’re infectious with Covid have gone down a lot,” said Dr. Robert Wachter, the chair of the medicine department at the University of California, San Francisco. “But you probably should wear a mask that day because you have something.”

And, remember, the result of your home test is just one piece of information. If you haven’t left the house in weeks, your negative result after a few tests is probably accurate. If you have symptoms and you’ve been spending time in bars or a family member has been exposed to Covid, you should be more cautious, even if the initial results are negative. It may be that you tested too early and that your viral load isn’t high enough to be detected.

When Dr. Jillian Horton, an internal medicine doctor in Winnipeg, started feeling ill, she was pretty sure she had Covid. Her husband had been exposed and had symptoms, too. She decided to conduct an experiment of one, testing herself several times over the course of a few days to track the dynamics of the virus. “With my husband testing positive and myself very symptomatic, I was sure I had Covid,” Dr. Horton said. “I was curious to see what I could pinpoint in terms of when I might flip positive.”

Dr. Horton’s husband became ill on a Friday night, and that evening she tested negative. On Saturday, she began to feel sick and tested herself three times throughout the day. All three results were negative.

By Sunday morning, she woke up and was feeling worse. At 6 a.m. she tested and saw a faint line on the test — what she called a “weak positive.” She took two more tests on Sunday and both were negative.

On Monday morning, she tested again, and the test rapidly turned positive.

What is notable about Dr. Horton’s experiment is that if she had tested at a different time on Sunday, she may never have discovered the weak positive. Her immune system was clearly battling the virus, as evidenced by her two negative test results later in the day.

Dr. Horton noted that testing at the right time to catch a high viral load was similar to putting a net in a stream. If the fish aren’t there, you won’t catch anything. But if you time it so that the fish are plentiful, you’ll catch your dinner.

Dr. Horton said she was concerned that too many people think the tests aren’t working when, in fact, they are a useful tool if you understand how to use them. They are ideal for “ruling in” Covid, but you have to consider more information when evaluating a negative test.

“So often I hear people say, ‘The test is useless,’” Dr. Horton said. “What my experience illustrated is that when you have symptoms, the tests are really ‘rule-in’ tests. I think of those two days when I was so symptomatic. I had one positive test and five negative tests. There was only one moment in there where I was more infectious.”

Linsey Marr, a professor of civil and environmental engineering at Virginia Tech and one of the world’s leading experts on viral transmission, said she assumed her daughter had Covid even after a rapid test came back negative. The child had a fever and sore throat, and she had been exposed to Covid through her gymnastics team.

But testing proved useful for knowing that her daughter wasn’t highly contagious, which helped Dr. Marr’s family know how to manage the risk. “We knew we needed to be careful,” Dr. Marr said. “But we didn’t have to totally put her in jail. The test told us that the viral load was not high enough that we had to lock her in her room and be that worried about all of us getting it.” Instead, the family wore masks and opened windows to improve ventilation.

Kristina Kasparian, who works from home in Montreal, believes she may have gotten Covid from her husband, who is a schoolteacher. They disagreed on whether a home test he took showed a faint positive. But a few days later she woke up with tightness in her chest and a sore throat. Her test was positive, and her husband has continued to test negative.

“It’s great to have this tool, but it’s such a variable snapshot in time,” she said.

Dr. Mina said that despite the limitations, people would benefit from frequent testing any time they suspect they have been exposed, have symptoms or want to be sure they are not infectious before spending time with a person at high risk. He also recommends testing before you start interacting with others again to be sure you’re not still infectious.

“These are tools that have massive benefit during a pandemic like this,” Dr. Mina said. “They will catch you when you’re most infectious. They will even catch you most of the time when you’re just slightly infectious. They will catch almost everyone when they have a high enough viral load to spread. But it won’t be perfect.”

Does the bivalent booster entirely replace the other boosters?

Credit...Jamie Kelter Davis for The New York Times

The new booster shot is a bivalent vaccine, meaning that it targets two versions of the coronavirus: the original strain and the Omicron subvariants BA.4 and BA.5, which became the dominant subvariants in the United States over the summer. The previous booster shot targeted only the original version of the virus.

On Sept. 1, the new shot became the only booster recommended for people ages 12 and older.

If you are being vaccinated against Covid for the first time, you will, however, receive the original vaccines that were introduced in late 2020.

Can you get the flu shot and the new booster at the same time?

Credit...Alessandro Grassani for The New York Times

Yes. Some public health officials are strongly recommending getting both the flu shot and the new bivalent booster at once — Dr. Ashish Jha, who leads the White House’s pandemic response, remarked in a press briefing that “God gave us two arms: one for the flu shot and the other one for the Covid shot.”

Combining vaccines, in general, is not unusual: children often receive multiple shots at once, said Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco. The Food and Drug Administration recently authorized the bivalent vaccine for children as young as 5, who can also get their flu shot at the same time, Dr. Chin-Hong said. And getting two shots at the same time means you’re less likely to forget, or put off, either one, he added. “Convenience trumps everything,” he said.

Most people will want to get one shot in each arm, Dr. Chin-Hong said, but you can receive both vaccines in the same arm — you just might be extra sore. “It’s personal preference — there’s no medical reason to do it one way or another,” said Dr. Adam Ratner, a pediatric infectious disease specialist at N.Y.U. Langone.

People who opt for two vaccines at once might experience more side effects, which are similar for both shots: tenderness at the injection site, headaches, fatigue. A small number of people may develop a fever.

If you want to spread out your shots, you may want to schedule your flu shot for later in the fall, so that protection from the vaccine kicks in when cases begin to rise in the winter. You can also monitor flu activity in your state, through the Centers for Disease Control and Prevention’s influenza surveillance reports, to assess whether you want to get the shot now or later.

Do boosters and prior infections protect against BQ.1 and BQ.1.1?

Credit...Kenny Holston for The New York Times

If you were infected with a previous version of Omicron recently, you can still become reinfected with BQ.1 and BQ.1.1, said Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco. However, a previous infection does confer some additional protection, he added — but that protection is unlikely to last beyond three months.

“No one’s going to be immune from re-infection,” said Dr. Steven Gordon, an infectious disease specialist at the Cleveland Clinic. “We can safely say that.”

The bivalent booster, which became available to adults in September, was designed to target BA.4 and BA.5, which were the dominant versions of the coronavirus at the time, but have tapered out as BQ.1 and BQ.1.1 have ascended. Still, the newest booster shots are likely to offer some protection against illness with these new subvariants, said Dr. Kelly Gebo, an infectious disease specialist at Johns Hopkins Medicine. Researchers aren’t sure just how substantial that protection is.

How long should I wait to get a bivalent booster if I recently had a shot or contracted Covid?

Credit...Erika P. Rodriguez for The New York Times

In August, the Food and Drug Administration authorized updated booster shots for people who are at least two months out from their last Covid shot (whether it was the original vaccine or a booster). You might want to wait longer between shots, though. While an advisory panel to the Centers for Disease Control and Prevention voted to recommend the same interval between doses, several members voiced concerns.

Doctors and immunologists said that, in general, people should wait four to six months after immunization to get a booster. Likewise, if you were recently infected with the coronavirus, you might want to wait that same amount of time before getting another shot.

That’s because your body will probably not generate much of an immune response so soon after a previous encounter with the virus, Aubree Gordon, an epidemiologist at the University of Michigan, said. “Your immunity level is so high that you’ll just neutralize immediately the antigen that’s being produced — you kind of reach a ceiling,” she said. “You don’t have that much higher to go.”

And keep in mind that once you do get the new booster, it typically takes around one to two weeks for your antibodies to kick in, Dr. Gordon said.

What antiviral treatments are available and do I qualify for them?

There are two oral antiviral therapies currently available to treat Covid-19 in the United States.

One, called Paxlovid, was developed by Pfizer and was the first oral treatment authorized for high risk Covid-19 patients ages 12 and older in December. It is prescribed as three pills taken twice a day for five days.

The second drug, called molnupiravir, was developed by Merck and was granted emergency use authorization just one day after the Pfizer treatment in December. Molnupiravir treatment consists of four pills taken twice a day for five days and is available for high-risk adults ages 18 and up.

The Food and Drug Administration has also cleared an intravenous antiviral medication from Gilead Sciences called remdesivir, which is sold under the brand name Veklury, but it is most often administered at a clinic or an infusion center.

To get these treatments you must test positive with a P.C.R. or rapid test. This can be done at home, at a regular health care provider’s office, at a testing site or at one of the pharmacy chains, community health centers, long-term-care facilities or Veterans Affairs clinics participating in the “test to treat” program.

If you test positive at a participating location that dispenses antivirals and has an authorized medical provider, you can get a Covid-19 pill prescription (if you’re eligible) and fill it on the spot. If you test positive at a different testing site or through an at-home testing kit, you can schedule an online or in-person visit with a provider at a “test to treat” location to get and fill a prescription.

And just like with other medications, your regular health care provider can call in a prescription to a pharmacy for you, said Kuldip Patel, the senior associate chief pharmacy officer at Duke University Hospital in North Carolina. You can use the Covid-19 therapeutics locator to find out which pharmacies stock the drugs near you.

What should I watch out for if I’m worried about Paxlovid rebound?

Credit...Wolfgang Rattay/Reuters

Reports of “Paxlovid rebound” popped up in the spring of 2022, as some people who had taken the antiviral medication experienced a recurrence of Covid symptoms, days after their infection appeared to have cleared up. But that rebound effect isn’t limited to people who have taken Paxlovid: a study this past fall found that symptoms can flare up again even in people who did not take the antiviral medication.

Those who have taken Paxlovid and are concerned about a potential rebound should watch out for returning symptoms in the week or so after they test negative. But “people should not be swabbing themselves like there’s no tomorrow if they’re feeling better,” said Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco.

Only a small fraction of people who take Paxlovid report a rebound, said Dr. Steven Gordon, an infectious disease specialist at the Cleveland Clinic; a study published in June found that of 13,644 adult coronavirus patients who took Paxlovid or another treatment, Molnupiravir, about 5 percent tested positive again within 30 days and 6 percent experienced symptoms again. And Paxlovid rebound is more likely in people who are older or have compromised immune systems, said Dr. Kelly Gebo, an infectious disease specialist at Johns Hopkins Medicine.

Those who do experience a recurrence of symptoms typically do so within a few days or a week, said Dr. Gebo. If you feel a sore throat or runny nose coming back, you may want to take a rapid antigen test, she advised. The Centers for Disease Control and Prevention recommend that anyone who experiences a rebound, whether or not they have taken Paxlovid, should isolate from others.

Does my mask protect me if nobody else is wearing one?

While it’s true that masks work best when everyone around you is wearing one, there is also plenty of evidence showing that masks protect the wearer, even when others around them are mask-free.

The amount of protection depends on the quality of the mask and how well it fits. Health experts recommend using an N95, KN95 or KF94 to protect yourself.

Other variables, such as how much time you are exposed to an infected person and how well a space is ventilated also will affect your risk.

“I know everyone talks about planes, but I would say buses are probably the riskiest, then trains and then planes, in order of highest to lowest,” said Linsey Marr of Virginia Tech, an expert in airborne transmission of viruses.

“People talk about planes having great ventilation filtration, and they do and that greatly helps reduce the risk of transmission,” she added. “But the virus is going to be in the air, no question in my mind, because there’s still large numbers of cases.”

There is also real-world data supporting the protective effects of masking in other indoor locations. A 2020 investigation of a hotel outbreak in Switzerland, for instance, found that several employees and a guest who tested positive for the coronavirus were wearing only face shields (with no masks); those who wore masks were not infected.

And a Tennessee study found that communities with mask mandates had lower hospitalization rates than areas where masks weren’t required.

A number of laboratory studies, too, have documented that a mask protects the person who is wearing it, though the level of that protection can vary depending on the type of mask, the material it’s made from, the experimental setup and how particle exposure was measured.

But the bottom line of all the studies is that a mask reduces the potential exposure of the person wearing it.

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Dr. Marr recommends wearing the highest-quality mask possible when you can’t keep your distance or be outdoors — or when nobody around you is masking up. That means an N95 or equivalent.

Sharon Otterman contributed reporting.

How often can you be infected with the coronavirus?

A Covid testing site in San Diego last year. Earlier in the pandemic, experts thought that immunity from vaccination or previous infection would forestall reinfections, but Omicron has changed that.
Credit...Ariana Drehsler for The New York Times

A virus that shows no signs of disappearing, variants that are adept at dodging the body’s defenses, and waves of infections two, maybe three times a year — this may be the future of Covid-19, some scientists now fear.

The central problem is that the coronavirus has become more adept at reinfecting people. Already, those infected with the first Omicron variant are reporting second infections with the newer versions of the variant — BA.2 or BA2.12.1 in the United States, or BA.4 and BA.5 in South Africa.

Those people may go on to have third or fourth infections, even within this year, researchers said in interviews. And some small fraction may have symptoms that persist for months or years, a condition known as long Covid.

“It seems likely to me that that’s going to sort of be a long-term pattern,” said Juliet Pulliam, an epidemiologist at Stellenbosch University in South Africa.

“The virus is going to keep evolving,” she added. “And there are probably going to be a lot of people getting many, many reinfections throughout their lives.”

It’s difficult to quantify how frequently people are reinfected, in part because many infections are now going unreported. Dr. Pulliam and her colleagues have collected enough data in South Africa to say that the rate is higher with Omicron than seen with previous variants.

This is not how it was supposed to be. Earlier in the pandemic, experts thought that immunity from vaccination or previous infection would forestall most reinfections.

The Omicron variant dashed those hopes. Unlike previous variants, Omicron and its many descendants seem to have evolved to partially dodge immunity. That leaves everyone — even those who have been vaccinated multiple times — vulnerable to multiple infections.

“If we manage it the way that we manage it now, then most people will get infected with it at least a couple of times a year,” said Kristian Andersen, a virologist at the Scripps Research Institute in San Diego. “I would be very surprised if that’s not how it’s going to play out.”

The new variants have not altered the fundamental usefulness of the Covid vaccines. Most people who have received three or even just two doses will not become sick enough to need medical care if they test positive for the coronavirus. And a booster dose, like a previous bout with the virus, does seem to decrease the chance of reinfection — but not by much.

At the pandemic’s outset, many experts based their expectations of the coronavirus on influenza, the viral foe most familiar to them. They predicted that, as with the flu, there might be one big outbreak each year, most likely in the fall. The way to minimize its spread would be to vaccinate people before its arrival.

Instead, the coronavirus is behaving more like four of its closely related cousins, which circulate and cause colds year round. While studying common-cold coronaviruses, “we saw people with multiple infections within the space of a year,” said Jeffrey Shaman, an epidemiologist at Columbia University in New York.

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Credit...Veasey Conway for The New York Times

If reinfection turns out to be the norm, the coronavirus is “not going to simply be this wintertime once-a-year thing,” he said, “and it’s not going to be a mild nuisance in terms of the amount of morbidity and mortality it causes.”

Reinfections with earlier variants, including Delta, did occur but were relatively infrequent. But in September, the pace of reinfections in South Africa seemed to pick up and was markedly high by November, when the Omicron variant was identified, Dr. Pulliam said.

Reinfections in South Africa, as in the United States, may seem even more noticeable because so many have been immunized or infected at least once by now.

“The perception magnifies what’s actually going on biologically,” Dr. Pulliam said. “It’s just that there are more people who are eligible for reinfection.”

The Omicron variant was different enough from Delta, and Delta from earlier versions of the virus, that some reinfections were to be expected. But now, Omicron seems to be evolving new forms that penetrate immune defenses with relatively few changes to its genetic code.

“This is actually for me a bit of a surprise,” said Alex Sigal, a virologist at the Africa Health Research Institute. “I thought we’ll need a kind of brand-new variant to escape from this one. But in fact, it seems like you don’t.”

An infection with Omicron produces a weaker immune response, which seems to wane quickly, compared with infections with previous variants. Although the newer versions of the variant are closely related, they vary enough from an immune perspective that infection with one doesn’t leave much protection against the others — and certainly not after three or four months.

Still, the good news is that most people who are reinfected with new versions of Omicron will not become seriously ill. At least at the moment, the virus has not hit upon a way to fully sidestep the immune system.

“That’s probably as good as it gets for now,” Dr. Sigal said. “The big danger might come when the variant will be completely different.”

Each infection may bring with it the possibility of long Covid, the constellation of symptoms that can persist for months or years. It’s too early to know how often an Omicron infection leads to long Covid, especially in vaccinated people.

To keep up with the evolving virus, other experts said, the Covid vaccines should be updated more quickly, even more quickly than flu vaccines are each year. Even an imperfect match to a new form of the coronavirus will still broaden immunity and offer some protection, they said.

“Every single time we think we’re through this, every single time we think we have the upper hand, the virus pulls a trick on us,” Dr. Andersen said. “The way to get it under control is not, ‘Let’s all get infected a few times a year and then hope for the best.’”

What can you do to reduce your risk of reinfection?

Many of the tools and behaviors that help protect against infection can still help you avoid reinfection, Dr. Abu-Raddad said. “There is no magical solution against Covid reinfection.”

Getting vaccinated and boosted, for example, is a good idea even after you’ve had Covid. You only need to wait a few weeks after an infection to get a shot. The vaccines will bolster your antibody levels, and research shows that they are effective in preventing severe outcomes if you get sick again. “Scientific confidence in vaccine-induced immunity was and is much higher than infection-induced immunity,” Dr. Crotty said.

Additional measures, like masking indoors and in crowded spaces, social distancing and improving ventilation where possible, can provide another layer of protection. But because most people and communities have largely dropped these protections, it is up to individuals to decide when to adopt extra precautions based on their risk of getting Covid and how much they’d like to avoid it.

“If you had an infection just last week, you probably don’t have to mask up,” Dr. Adalja said. “But as a month or so passes from your infection and new variants start circulating in the U.S., it may make sense for high risk individuals to do that. People who are trying to avoid getting Covid because they’re going on a cruise soon or because they need a negative P.C.R. test for some other reason may consider taking precautions. Covid protections don’t have to be one-size-fits-all.”

What should I do if I was exposed to someone with Covid?

If you are an adult who’s been boosted or are a fully vaccinated child, you don’t need to quarantine after a potential exposure. But you should get tested at least five days after your exposure and wear masks around other people for 10 days.

If you’re unvaccinated, quarantine for five days after exposure and then get tested. Wear masks around other people for 10 days. This also applies to those who are eligible for booster shots but have not yet received them.

Dani Blum and

Will subsequent infections be more or less severe?

The good news is that your body can call on immune cells, like T cells and B cells, to quash a reinfection if the virus sneaks past your initial antibody defenses. T cells and B cells can take a few days to get activated and start working, but they tend to remember how to battle the virus based on previous encounters.

“Your immune system has all kinds of weapons to try and stop the virus even if it gets past the front door,” said Shane Crotty, a virologist at the La Jolla Institute for Immunology in California.

Many of these immune cells build up their protections iteratively, Dr. Crotty said. That means that people who are vaccinated and boosted are especially well equipped to duke it out with the coronavirus. Similarly, people who have been infected before are able to keep the virus from replicating at high levels if they get reinfected. And most people who have logged encounters with both the vaccine and the coronavirus build up a hybrid immunity that may offer the best protection.

The result is that second or third infections are likely to be shorter and less severe.

Dr. Abu-Raddad, who has been tracking reinfections among large groups of people in Qatar, has already started seeing this promising pattern in patient records: Of more than 1,300 reinfections that his team identified from the beginning of the pandemic to May 2021, none led to hospitalization in an I.C.U., and none were fatal.

But just because reinfections are less severe, it doesn’t mean that they are not terrible. You may still run a fever and experience body aches, brain fog and other symptoms. And there’s no way of knowing if your symptoms will linger and become long Covid, Dr. Adalja said.

It is possible that each Covid infection forces you into a game of Russian roulette, though some researchers hypothesize that the risk is highest right after your first infection. One of the risk factors for long Covid is having high levels of virus in your system early in an infection, and you are likely to have such a high viral load the first time you are infected, Dr. Abu-Raddad said. In subsequent infections, your body is better prepared to fight off the coronavirus so you may be able to keep the virus at low levels until it is completely cleared, he said.

How long will my immunity last after getting Covid?

Before Omicron, reinfections were rare. A team of scientists, led by Laith Abu-Raddad at Weill Cornell Medicine-Qatar, estimated that a bout with Delta or an earlier coronavirus strain was roughly 90 percent effective in preventing a reinfection in both vaccinated and unvaccinated people. “But Omicron really changed that calculus,” said Dr. Abu-Raddad, an infectious disease epidemiologist.

After Omicron emerged, prior infections only provided about 50 percent protection against reinfection, Dr. Abu-Raddad’s study showed. The coronavirus had acquired so many mutations in its spike protein that newer versions became more transmissible and better able to evade immunity. That means you can catch a version of Omicron after recovering from an older, non-Omicron variant. You can even get sick with one of the newer Omicron subvariants after getting over a different version of it.

Other factors also increase your vulnerability to reinfection, starting with how long it has been since you had Covid. Immune defenses tend to wane after an infection. A study published in October 2021 estimated that reinfection could occur as soon as 3 months after contracting Covid-19. While these findings were based on the genome of the coronavirus and accounted for expected declines in antibodies that could fight off the virus, the study did not account for new variants like Omicron that were radically different from older variants. Because of how different Omicron is, your protection may wane even sooner. In a study published in February that has not yet been peer-reviewed, scientists from Denmark found that some people got reinfected with the BA.2 sublineage of Omicron as soon as 20 days after they got infected with the original Omicron BA.1.

Because the virus is infecting more people now, your chances of being exposed and getting reinfected are also higher, Dr. Abu-Raddad said. And while it’s unclear if some people are simply more susceptible to Covid-19 reinfection, researchers are beginning to find some clues. People who are older or immunocompromised may make very few or very poor quality antibodies, leaving them more vulnerable to reinfection, Dr. Abu-Raddad said. And early research shows that a small group of people have a genetic flaw that cripples a crucial immune molecule called interferon type I, putting them at higher risk of severe Covid symptoms. Further studies could find that such differences play a role in reinfection as well.

For now, you should treat any new symptoms, including a fever, sore throat, runny nose or change in taste or smell, as a potential case of Covid, and get tested to confirm if you are positive again.

How can I find a quality mask (and avoid counterfeits)?

The fast-spread of Omicron and its subvariants has prompted many people to try to upgrade to a higher-quality mask. But that’s easier said than done.

Anyone who has shopped for a mask online or in stores has discovered a dizzying array in a variety of shapes, sizes and colors. Knowing which mask to pick and making sure it’s not a counterfeit requires the sleuthing skills of a forensic investigator. And once you choose one, it’s still a gamble; many people discover they’ve ordered a mask that’s too big or too small for their face or just doesn’t fit right.

“No one has made this easy, that’s for sure,” said Bill Taubner, president of Bona Fide Masks, the exclusive distributor in the United States for both Powecom and Harley KN95 masks, which are from China. “A lot of people end up doing a lot of research.”

Unlike cloth masks, high-quality masks — called N95s, KN95s and KF94s — are made with layers of high-tech filtering material that trap at least 94 to 95 percent of the most risky particles. Early in the pandemic, high-quality medical and respirator-style masks were in short supply. Now the problem is there are so many different masks for sale, it’s tough to know which ones have been tested and certified by government agencies, and which are counterfeit. Testing studies have found that many counterfeit masks don’t even offer the same level of protection as a cloth mask. We interviewed mask manufacturers, importers, public health officials and independent researchers for advice on choosing a quality mask. Here’s a guide.

Masks come in different shapes and sizes. You’ll find “cup” style masks, “duck bill” masks and “flat-fold” masks. The best mask is the one that fits snugly against your face and is comfortable. Start by ordering in small quantities and try different styles to find the best one for your face. Many masks are described as “one size fits most.” But some come in small or larger sizes. “You’re not getting the full benefit of a respirator if you put it on and it’s not forming a seal to your face,” said Nicole Vars McCullough, vice president for personal safety at the 3M Company, the largest U.S. manufacturer of N95 masks.

N95 respirator

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Credit...Sarah Kobos/Wirecutter

The N95 respirator mask is regulated by the National Institute for Occupational Safety and Health (NIOSH), a division of the Centers for Disease Control and Prevention. Almost all N95 masks use head straps — two elastic bands that wrap behind the head. If a mask claiming to be an N95 has ear loops, it’s most likely a fake. The C.D.C. has a guide for spotting fake N95s.

KN95 respirator

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Credit...Sarah Kobos/Wirecutter

The KN95 is similar to the N95, but it has ear loops and is made to meet Chinese standards for medical masks. Some people prefer them for comfort, and because they come in smaller sizes. While you can find legitimate KN95 masks, the supply chain is riddled with counterfeits and there’s little regulation or oversight of the product. One study found that 60 percent of the supply of KN95s in the United States are counterfeit. Keep reading for ways to spot them.

KF94

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Credit...Sarah Kobos/Wirecutter

The KF94 is a high-quality mask that folds flat and is made in Korea. It is designed specifically for the consumer market. The KF stands for “Korean filter,” and the 94 means it filters 94 percent of particles. The masks are heavily regulated in Korea, which lowers the risk of counterfeits. However, some fake masks made in China may be labeled KF94, so shoppers still need to do their homework.

Masks for children

The mask market is particularly tricky for parents trying to find masks for children. No N95 mask has been approved for children, so any mask that claims to be an N95 for kids is a fake. However, N95s do come in S/M sizes that might work for some older children. KN95 and KF94 masks have styles made for children, so once you find one, you need to go through the same vetting process that you would use for an adult mask, using the links below.

Big retailers like Home Depot and Lowes typically work directly with manufacturers approved by NIOSH or their distributors, so if you find an N95 mask in a major retail store you can be confident you’re getting the real thing. It’s a good idea to check manufacturer websites to see where they sell their products and who their authorized distributors are, Dr. McCullough said. 3M has a dedicated spot on its website to help consumers spot fake masks.

Finding a reliable mask on Amazon is trickier because you’ll see legitimate masks mixed in with counterfeits, although the differences won’t always be obvious. If you must use Amazon, try to shop directly in the on-site stores of mask makers like 3M or Kimberly-Clark. (You can usually find a link to a maker’s online store right below a product name.)

If you’re buying a KF94 on Amazon, look closely at the packaging to make sure it’s made in Korea and includes the required labeling (see below for more details). Aaron Collins, an engineer who routinely tests masks and who has gained a YouTube following as “Mask Nerd,” recommends buying KF94s from Korean beauty product importers like Be Healthy or KMact. Once you learn the names of a few KF94 manufacturers, you can try to find their websites to learn where they are sold. For instance, Happy Life lists its five U.S. distributors on its home page.

You can sometimes find N95 and KN95 masks for sale directly on the website of a mask maker, like Demetech and Armbrust USA. You can also look for companies that are exclusive distributors of KN95 masks, like Bona Fide Masks. The nonprofit site Project N95 is also a reliable place to shop. Many trusted sites are overwhelmed by demand right now, so you may encounter delays in fulfillment and shipping times.

Legitimate N95s and KN95s are required to have specific text stamped on the front of the mask. Although you may find one in a fun color, masks that are printed with fancy designs or don’t have text stamped on them are probably fake.

Your N95 should be stamped with “NIOSH,” as well as the company name, the model and lot numbers, and something called a “TC approval” number, which can be used to look up the mask on a list of approved ones. The C.D.C. has created an infographic showing you the printing to look for on your N95.

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Credit...Charlie Rubin for The New York Times

A legitimate KN95 should also be stamped with text, including the name of the manufacturer, the model and “GB2626-2019,” which is a reference to a quality control standard approved by the Chinese government. (If your mask has a GB number that ends in 2006, which is a previous standard, just check the expiration date.)

The KF94 won’t be stamped with text, but the package should say “Made in Korea” and include the product name, manufacturer and distributor name. Each mask should be packaged individually in a flat, glossy rectangular wrapper with a textured border. The package will also have an expiration date and a lot number printed on it. (Masks that carry an electrostatic charge all have expiration dates.) If your mask comes from a Korean importer, the information on the package will be in Korean, but many companies have begun to create English-language packaging.

A number of resources have sprung up to help people navigate the mask-buying process. Project N95 is a nonprofit known for vetting its mask suppliers. Mr. Collins, the Mask Nerd, has created a number of lists and resources for mask buyers. You can check out his Twitter feed, his YouTube channel and a spreadsheet he has created of nearly 450 different masks and how they performed in his tests.

Mr. Collins may be best known for his list of children’s masks. While there is no N95 mask for kids approved in the United States, mask makers in China and Korea have created KN95s and KF94s for children, including some with child-friendly colors and prints. Mr. Collins created a video “primer for parents” about finding a high-quality mask for kids that has more than 100,000 views.

“I had retired from mask testing,” Mr. Collins said, noting that he doesn’t receive any compensation for his work. “But I came out of retirement to do the kids video. The only place I’ve seen a list of test data is unfortunately me.”

Wirecutter, a product review site owned by The New York Times, has a guide for buying quality masks, one for buying children’s masks and a list of 12 red flags that might signal your mask is a counterfeit.

It’s not easy, but the C.D.C. has a few lists you can use to confirm a mask has been vetted. A note of caution: If you don’t find a particular mask, make sure you’ve looked it up the correct way, said Anne Miller, executive director of Project N95. For instance, a Gerson N95 mask won’t be found under the letter “G.” It’s listed under “L” because the full name of the company that makes it is Louis M. Gerson.

For N95 masks, go to the C.D.C.’s alphabetical list of NIOSH-approved respirators. You can also look up the TC approval number using the certified equipment list.

For KN95 masks, you can use two checklists from the Food and Drug Administration. The F.D.A. created these lists early in the pandemic, when the agency issued an emergency use authorization that allowed health workers to use KN95 masks because of a shortage of N95s. Now that the N95 supply is adequate, the agency has revoked the authorization for these workers, but other people can still use KN95s. While the list is now a bit outdated, finding your mask on it adds reassurance that it’s less likely to be counterfeit — with the caveat that there’s no longer official U.S. oversight for any of these firms. You’ll need to scroll down to find the list and search box.

Use this F.D.A. list to find KN95 masks made in China, and this list for KN95 masks made in other countries.

Jin Yu Young contributed to this report.

What is long Covid? How will I know if I have it?

Among the many confounding aspects of the coronavirus is the spectrum of possible symptoms, as well as their severity and duration. Some people develop mild illness and recover quickly, with no lasting effects. But studies estimate that 10 to 30 percent of people report persistent or new medical issues months after their initial coronavirus infections — a constellation of symptoms known as long Covid. People who experience mild to moderate illness, as well as those without any underlying medical conditions, can nonetheless experience some debilitating long-term symptoms, including fatigue, shortness of breath, an erratic heart rate, headaches, dizziness, depression and problems with memory and concentration.

Such lingering medical issues are so varied that one study by a patient-led research group evaluated 203 symptoms that may fluctuate or even appear out of the blue after people seem to have recovered.

There is little consensus on the exact definition of long Covid, also known by the medical term PASC, or post-acute sequelae of Covid-19. The World Health Organization says long Covid starts three months after the original bout of illness or positive test result, but the Centers for Disease Control and Prevention sets the timeline at just after one month. For now, doctors must rely on their patients’ descriptions of symptoms and rule out alternative explanations or causes. Some post-Covid clinics have multidisciplinary teams of specialists evaluate patients to figure out the best treatment options.

Can vaccines protect against long Covid?

The picture is still coming into focus, but several studies suggest that getting a Covid vaccine can reduce — but not eliminate — the risk of long-term symptoms. The United Kingdom’s Health Security Agency conducted an analysis of eight studies that had looked at vaccines and long Covid before mid-January. Six found that vaccinated people who became infected with the coronavirus were less likely than unvaccinated patients to develop symptoms of long Covid. The remaining two studies found that vaccination did not appear to conclusively reduce the chances of developing long Covid. In that analysis, one study, which examined about 240,000 U.S. patients but has not been peer-reviewed, found that those who had received even one dose of a Covid vaccine before their infections were seven to 10 times less likely than unvaccinated patients to report symptoms of long Covid 12 to 20 weeks later. But another large study of electronic patient records at the U.S. Veterans Health Administration, also not yet peer reviewed, found that those who were vaccinated had only a 13 percent lower risk than unvaccinated patients of having symptoms six months later.

What are the side effects of the vaccines in young kids?

The data so far suggest that the side effects in younger kids are milder than those in older kids, probably because a lower dose of the vaccine is given, Dr. Shirley said. Among children under 5, “the side effects were the sorts of things that we might expect in children after receiving a vaccine,” she added, including increased fussiness, sleepiness and pain at the injection site. Comparing the two vaccines, Pfizer’s resulted in fewer side effects overall, probably because it uses such a low dose.

No children in the vaccine trials developed heart issues like myocarditis, a form of heart inflammation that was seen in a small number of older children who received the vaccine, Dr. Shirley said, but this could be because the trials were not big enough to detect rare side-effects. It’s possible there will be some cases once the vaccines are given to enough kids, but experts don’t expect to see a significant number, because myocarditis “occurs more frequently in teenagers and young adults than younger kids,” said Dr. Ibukun Kalu, an infectious disease pediatrician at the Duke University School of Medicine. “I would not expect high rates of vaccine-related myocarditis in the under 5s,” she added. Dr. Kalu also pointed out that the risk of myocarditis is much higher among kids who catch Covid-19 than it is among those who get the vaccine.

It’s important to note that when the F.D.A. did not authorize the two-dose Pfizer vaccine back in February, that was because it didn’t work well enough, not because of any safety issues. (And that’s ultimately why the vaccine now has a three-dose regimen.)

Covid-19 symptoms are often mild in young kids, and they can get the virus even if they’re vaccinated, so what’s the point of vaccinating my young child?

It’s true that Covid-19 is far less risky for kids than it is for those who are older. But more than 440 children aged 4 and under have died from Covid-19 since January 2020, and the infection is “one of the top 10 causes of death in children in the United States,” said Dr. Yvonne Maldonado, a pediatric infectious disease physician at Stanford Medicine who chairs the American Academy of Pediatrics’ committee on infectious diseases. Also, Covid-related hospitalization rates are higher for children 4 and younger than they are for older children, and more than half of pediatric hospitalizations among kids ages six months through 4 years occur in children with no known underlying risk factors. “I’ve had a number of friends who are health care providers whose children have wound up in the hospital, some on oxygen in the I.C.U., who have no risk factors,” Dr. Maldonado said.

“Vaccines are the most effective way that we have as clinicians to help prevent patients from developing severe forms of Covid,” Dr. Shirley said — and that includes little kids.

Should you take Paxlovid if you are mildly ill?

A blue and gold packet of Paxlovid pills sits on a red background with three pills sitting to the right of it
Credit...Stephanie Nano/Associated Press

It is becoming harder to avoid infection, and reinfection, from the coronavirus with each variant that emerges. Omicron offshoots like the latest one, the XBB.1.5 subvariant, are better at dodging antibodies. But Covid cases also seem to be growing milder, either because new variants are less likely to go deep into the lungs or because most people have been vaccinated, exposed or both.

Which raises the question: Do mild cases of Covid warrant treatment with an antiviral medication like Paxlovid?

In many cases, they do. Paxlovid is known to reduce the severity of illness and even lower the risk of developing long-term symptoms such as chronic fatigue, muscle pain, kidney disease, heart disease, blood clotting problems and neurocognitive impairments. Research has shown that it can offer these benefits for both vaccinated and unvaccinated people, those who are experiencing their first infection and those who have had a reinfection.

Paxlovid’s ability to lower the odds of hospitalization and death is well documented. Studies conducted before the drug was authorized in December 2021 showed that Paxlovid reduced these severe outcomes by up to 89 percent in unvaccinated people. While data from last year was slightly less impressive in vaccinated people, Paxlovid still decreased the odds of hospitalization and death by about 57 percent.

Paxlovid stops the coronavirus from replicating in cells. Scientists hypothesize that by reducing the viral load in the body quickly, Paxlovid hinders many problems linked to severe outcomes and long-lasting symptoms, like damage to blood vessels, widespread inflammation and overactivation of the immune system.

In a study published online in November and currently undergoing peer review, researchers found that among patients in the Veterans Health Administration system who had at least one risk factor qualifying them for antiviral treatment, those who took Paxlovid within five days of testing positive were 26 percent less likely to develop long Covid symptoms. Yet only about 15 percent of patients eligible for the drug took it. Other studies have suggested an even lower uptake.

Many experts agree that more people should be taking Paxlovid and that the treatment should be considered even for mild cases of Covid-19.

“A drug that you don’t take surely can’t prevent long Covid or reduce your likelihood of serious illness, hospitalization or death,” said Michael Osterholm, an epidemiologist and the director of the Center for Infectious Disease Research and Policy at the University of Minnesota.

“The threshold for giving Paxlovid should be lower and more people should be getting it, because it’s really not harmful,” said Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco.

All adults over 50 are eligible for the drug, as are children and adults 12 years and older who weigh at least 88 pounds and have one or more risk factors for severe Covid. People in these categories should talk to their doctor about taking Paxlovid if they develop any symptoms. The antiviral treatment is only given if a prescription can be filled within the first five days of symptom onset. In particular, studies show that adults over 65 benefit the most from taking Paxlovid. Their age puts them at higher risk for poor outcomes regardless of whether they have other medical conditions, Dr. Chin-Hong said.

The evidence is less clear on whether Paxlovid is worth taking for people under 50 who are not immunocompromised and do not have medical conditions like cancer, chronic lung disease, diabetes or many others.

“It is a personal decision between the person who’s affected and their provider whether to take Paxlovid or not,” said Dr. Ziyad Al-Aly, a clinical epidemiologist at Washington University in St. Louis and chief of research at the Veterans Affairs St. Louis Healthcare System. When a younger colleague recently had Covid, for instance, Dr. Al-Aly, who led the November study on long Covid, recommended that the person take the antiviral because it might still provide some of the same benefit against long-term symptoms.

Many doctors aren’t prescribing Paxlovid. And patients who do have access to the drug are refusing it.

“It is really baffling,” Dr. Al-Aly said. “But that’s what’s happening in the U.S. — Paxlovid is being remarkably underutilized.”

The treatment, which has been available for more than a year and is provided free by the federal government, has been plagued with public relations problems from the beginning.

For the first few months after it received emergency-use authorization from the Food and Drug Administration, Paxlovid supplies were hard to find. Then, patients who took the drug began reporting a bitter or metallic taste that stuck with them throughout the treatment. Several high-profile cases of Paxlovid rebound, or the recurrence of Covid symptoms, also led to the speculation that this unwanted side effect was fairly common.

“There have now been several studies, and there’s such good information that there’s very little difference in the rate of rebounds among those who take Paxlovid and those who don’t. Yet that myth continues,” Dr. Osterholm said.

Who should get the antiviral treatment has also remained a source of confusion for both patients and health care providers, Dr. Osterholm said. Because the drug is provided under an emergency-use authorization by the F.D.A., doctors don’t typically prescribe it outside of the stated eligibility criteria. (Prescribers tend to be more flexible with a fully approved drug. Some approved medicines can be prescribed or refilled early if you are going on vacation, for instance, but many people traveling abroad, including Dr. Osterholm, have found it difficult to get a hold of Paxlovid in advance.)

Another source of confusion is interactions that Paxlovid can have with many drugs, including statins, beta blockers, blood thinners, antipsychotic medicines, seizure medicines, certain migraine medicines and hormonal birth control. It is likely that the long list of potential interactions puts many people off. But a doctor can help patients take Paxlovid safely and avoid side effects in several cases, Dr. Osterholm said. For example, patients can stop taking statins while on Paxlovid, he said, and that is “not going to have a material impact on your health.”

Several experts said they knew of cases where primary care providers dissuaded patients from taking Paxlovid because the doctor thought that the patient either did not qualify or did not need the treatment. Many may be under the false impression that you can take Paxlovid only if you have severe disease, Dr. Chin-Hong said, when, in fact, the drug is for anyone at risk of such disease.

In July, the F.D.A. revised Paxlovid’s emergency-use authorization so that pharmacists could prescribe the drug. But that has not had a significant impact on Paxlovid use, Dr. Chin-Hong said.

The problem is about to become much worse, Dr. Chin-Hong said. The U.S. government bought millions of Paxlovid pills at about $530 per course, a discount the drugmaker Pfizer gave them for purchasing in bulk. But government support for the medication is expected to run out in the middle of this year. When the drug enters the private insurance market, Pfizer could increase the price, making it inaccessible for the people at highest risk of severe Covid and the least able to afford treatment: seniors and the uninsured.

To improve access and uptake of the drug, Dr. Chin-Hong said, “we’re going to need systemic changes.”

Where do I report a positive home test?

There is no standardized system to easily report the results of your Covid-19 home test, and experts worry that this makes official case counts an unreliable measure of the coronavirus’s true toll. But that does not mean you can’t volunteer your test results through a few different reporting systems.

“We do need a better sense of the amount of Covid in the community as people and organizations try to plan their behavior,” said Dr. Robert Wachter, the chair of the medicine department at the University of California, San Francisco. “When I’m deciding whether to eat indoors, for example, I don’t care about hospitalization numbers. I want to know the chance that my waiter or table-mate has Covid.”

If you test positive at home, one way to share your result is directly through your test kit’s mobile app, Dr. Wachter said. Apps for some rapid test kits, like BinaxNOW, iHealth and Lucira, include a form or button to report your results after you’ve watched instructional videos and followed all the directions for collecting and testing your sample.

The Centers for Disease Control and Prevention also “strongly encourages” everyone who tests at home to report any positive results to their health care providers. Make sure you tell your doctor a few key details: the kind of test you took, the time you took it, the date you started experiencing symptoms and your vaccination status. Your doctor may then recommend taking a P.C.R. test for confirmation and can provide a medical report to help you take time off from work or school. Your doctor can also help you track new or concerning symptoms that you might have, give advice about antiviral treatments and clear you to return to work once you have fully recovered.

Another way to report your home test result is to contact your local public health department, though the exact method can vary depending on where you live. You can find your health department’s website and information through the directory for the National Association of County and City Health Officials.

Some public health departments, like the one in Marin County, Calif., use simple online forms for reporting results. Others, like in St. Louis County, Mo., offer multiple options to call in, email or submit results online. In Washington, D.C., you can use an iPhone or Android app, in addition to the Department of Health’s web portal.

Lastly, there is the option to participate in crowdsourcing platforms developed by infectious disease researchers specifically for tracking home test results, such as the website OutbreaksNearMe.org. Originally designed to track flu outbreaks, the site has expanded to help create maps and analyze Covid-19 case data submitted by volunteers. According to John Brownstein, an epidemiologist and chief innovation officer at Boston Children’s Hospital who helped develop the resource, the website also shares information with the C.D.C. and local public health agencies and makes it available to the public.

“Home tests represent a huge change in how quickly people can identify an infection, how quickly they can get care and access therapeutics,” Dr. Brownstein said. “They are going to be a core way that health care is delivered in the future, so we need to make sure that we in public health keep up with testing data.”