WHEN YOU TEST POSITIVE for Covid, you surely know by now that you can pass the virus along to others. But you might be unsure exactly how contagious you are at different stages of the illness—and when you’re no longer contagious.
“Well, that’s a great question, because most of our studies where we looked at how long people shed live virus, which is infectious, were with earlier variants,” says Thomas Russo, M.D., an infectious disease expert and professor at the University at Buffalo. “We don’t have any data on the circulating variants.”
But many of the general guidelines still apply, he says. You’re typically most contagious when your viral load is the highest, which research has shown to be day four after symptoms started. And the Centers for Disease Control and Prevention says you may still be contagious for up to 10 days.
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Covid continues to circulate, and new variants will likely continue to emerge. Dr. Russo says that means it’s still infectious and transmissible.
Cases will also probably go up heading into winter when the cooler temperatures keep people indoors in poorly ventilated spaces where the virus can easily spread, he adds. Plus, Covid is floating around along with the flu, and it’s possible to get both illnesses at the same time—so it’s important to get the updated Covid vaccine and flu shot.
“We want to forget about Covid, but unfortunately, it hasn’t forgotten about us, and it continues to evolve,” Dr. Russo says.
That’s why understanding when you’re most contagious when you have Covid is so crucial. Here’s what you should know about Covid’s contagiousness.
When do you become contagious with Covid?
It’s not fully clear when you start being contagious after being exposed to Covid. But, typically, you’re most contagious during the first five days of symptoms, says Vincent Covelli, M.D., a board-certified infectious disease physician at telemedicine platform PlushCare.
The CDC suggests that people infected with Covid who are asymptomatic or have mild symptoms should isolate for at least five days after symptoms start and wear a mask through day 10.
If you have moderate or severe symptoms, you should isolate for at least 10 days, but you might be infectious for longer and may need to isolate for up 20 days, the CDC says.
You tend to be most contagious when your viral load is the highest, Dr. Russo says. A study published in Clinical Infectious Diseases in 2023 found that viral loads of the Omicron variant peaked on the fourth day after symptoms started.
When do you stop being contagious?
Usually, most healthy people are no longer contagious 10 days after first testing positive for Covid, Dr. Covelli says.
“It’s recommended that a second rapid at-home COVID test be performed to document negativity,” he says. “It’s at this point that a person is likely no longer contagious to others.”
People who are immunocompromised may shed the virus for longer time periods when they have Covid, so they may be contagious for longer, Dr. Russo says. The CDC suggests that people who are moderately or severely immunocompromised need to isolate through day 20.
The best answer for when you’re no longer contagious depends on when your symptoms start or when you know you’ve been exposed. The CDC offers an online Isolation and Exposure Calculator to help you determine when you need to isolate and when you should be able to end isolation.
Are newer Covid variants more contagious than others?
Some variants are more contagious than others. Dr. Russo says Omicron and its variants were highly infectious. But the virus keeps evolving, and new strains emerge.
The current strains that are circulating include EG.5 (Eris), FL.1.5.1 (Fornax), and XBB.1.16, and they’re closely related to the omicron XBB.1.5 variant, which is the strain that the updated Covid vaccine targets.
These variants may still be transmissible even if you’re vaccinated, Dr. Covelli says. But, he adds, he’s seeing less severe symptoms from the new variants compared to the original Covid strains, including fewer patients with low oxygen levels and shortness of breath.
Are you less contagious if you’ve been vaccinated?
While the vaccines won’t always prevent Covid infections, Dr. Russo says you’ll likely have fewer days of symptoms if you get sick and shed less virus, so it’s possible that you could be less contagious. But, there’s no clinical data on the subject.
Still, it’s crucial to get the updated Covid vaccine. It can help reduce your risk of getting severely sick from Covid, being hospitalized, and getting long Covid.
“The earlier you get your vaccinations, the more time your body has to build up immunity,” Dr. Covelli says.
Erica Sweeney is a writer who mostly covers health, wellness and careers. She has written for The New York Times, HuffPost, Teen Vogue, Parade, Money, Business Insider and many more.