How can we prevent the winter “tripledemic” of respiratory viruses from destroying vacation travel and upcoming family gatherings? People know when they have covid symptoms, but do minor sniffles at the end of a coronavirus infection, for example, mean they’re still contagious?
So many Covid questions!
Now is a good time to dig deeper into what scientists know, and still don’t know, about how long people are infected with viral illnesses — Covid, flu, RSV — that are spreading in the United States.
How long am I contagious with Covid?
If you have been exposed to someone who is Covid-positive, symptoms of one of the omicron subvariants usually appear two to four days later.
How contagious you are and how much virus, known as your viral load, is in your body. Your viral load will likely peak soon after symptoms appear, according to Dr. Chanu Rhee, an infectious disease physician and associate professor of medicine at Harvard Medical School. This means that you are probably most contagious about a day before symptoms appear and for at least the first two or three days afterward.
As your immune system lowers your viral load, your infectiousness should decrease in tandem.
“If people are still very, very symptomatic, with a lot of coughing and a lot of upper respiratory tract symptoms, then you think they’re probably more infectious,” Dr. Lisa said. A. Cosimi, an infectious disease specialist at Harvard Medical School.
But deciding whether you’re still somewhat contagious during the final days of a Covid illness can be tricky.
the Centers for Disaster Control and Prevention recommends people with moderate to severe symptoms self-isolate for 10 days. If your Covid is a mild illness, the CDC advises that to protect others, you should consider yourself contagious for at least five days from the onset of symptoms — or five days after a positive test, which counts as the day zero.
A study of 66 people without Covid published in the New England Journal of Medicine in July found that the median time until participants were likely no longer infectious was six days when the delta variant of the virus was dominant and eight days during the omicron wave.
According to a October study out of 4,565 people with Covid, “overall, existing data suggest that infectivity (using viral culture as a proxy) beyond 10 days is possible although less common.”
Investigators have called for more research into whether people remain contagious after this point.
There have, however, been cases of immunocompromised people who have remained contagious for months, according to various infectious disease experts.
As far as using Covid tests to determine if someone is still contagious, PCR tests are good for diagnosing Covid. They are unreliable in determining ongoing infectiousness because they can detect fragments of the virus, which pose no risk of transmission to others, for weeks or months after infection.
Rapid home antigen tests aren’t perfect either. Researchers rely on what are called viral culture tests in which they take a swab of the coronavirus and see if they can grow the virus in the lab, as the best indicator of infectivity. But ordinary people do not have access to such tests.
In a recent to study Of 40 people with Covid, three quarters of them tested positive six days after their first positive test or the onset of their symptoms, whichever came first.
As part of the research, participants also received what are called viral culture tests in which scientists see if they can grow the virus taken from a swab in the lab. It is considered the best indicator of infectivity.
About half of this group had a negative virus culture test at the time, suggesting they were not contagious.
Cosimi, the Harvard Medical School infectious disease specialist, was lead author on the study and said that after the fifth day of Covid – if people test negative when they have improved but still have persistent symptoms – they are probably not contagious.
She also said that if people who are not immunocompromised feel well on day 11 but still test positive on an antigen test, “it is extremely unlikely” that they are still infectious.
According to the CDC, if you have no symptoms after day five, or if your Covid symptoms improve and you haven’t had a fever for 24 hours, you can end your isolation period.
From the sixth to the tenth day, you can go out but you must wear a mask.
You do not need to test to end your isolation period in these settings. The CDC says you can remove the mask sooner if you test negative on two consecutive rapid antigen tests 48 hours apart.
There is one condition, however.
“You should still wear a mask until day 10 because theoretically you’re still contagious, even if your level of infectiousness has gone down,” Rhee said.
How long am I contagious if I had Covid or am I fully vaccinated and have a breakthrough infection?
Many studies showed that vaccination helps the body eliminate the coronavirus more quickly.
Most studies, however, have involved patients infected with the older variants, Rhee said.
“The impact of prior immunity on infectivity is not as clear for omicron variants.”
On average, unvaccinated people do indeed take longer to beat the infection, said Dr. Yonatan H. Grad, associate professor of immunology and infectious diseases at Harvard TH Chan School of Public Health and lead author. of a recent article in the journal eLife in which he and his colleagues came to this conclusion.
We do not know the duration of infectivityGrad said in an email.
If I take Paxlovid, am I contagious?
A study published in Clinical Infectious Diseases in July found that taking Paxlovid speeds clearance of the coronavirus, which the authors say may reduce infectivity.
Recent to research questioned whether Paxlovid is causing viral rebound cases, since people who don’t take Paxlovid also rebound.
“What we don’t know is whether these rebounds are infectious or not,” said Dr. Donald Milton, professor of environmental and occupational health at the University of Maryland.
Therefore, the CDC recommends restarting the isolation clock on day zero in the event of a bounce.
How long am I contagious with the flu or other viral illnesses?
With the flu, RSV (respiratory syncytial virus) and the common cold, experts say, people are usually most contagious between a day or two before symptoms start and then for a few days afterwards.
The CDC recommends people with the flu stay home until at least 24 hours after their fever clears without using fever-reducing medication or after their symptoms improve, at least four to five days after getting sick.
A 2010 to study They identified a strong correlation between the decrease in flu symptoms, particularly fever, and a decrease in viral shedding, which indicates infectiousness.
“If you’re really sick, if you have a fever, you can be contagious for a bit longer,” said Aubree Gordon, associate professor of epidemiology at the University of Michigan School of Public Health. “The level of symptoms can be a guide to when you should stay home. But that doesn’t mean that if you have mild symptoms you aren’t contagious.
Classic cold symptoms include congestion, cough, runny nose and low fever. Some Cold symptoms can last 10 to 14 daysAccording to the CDC.
For colds – which for adults can include RSV, a virus that can pose a serious threat to children under 2 – Dr. David Strain, clinical lecturer at the University of Exeter said: “For the most part, you will only be contagious as long as you have symptoms.”
This article was originally published on NBCNews.com
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