Here's how to decide if you're safe to go out when you're recovering from omicron

The good news is, the numbers of COVID-19 cases are plummeting across the country. But there's still a stunning amount of virus spreading in many places, with more than 100,000 reported cases a day. If you have a current infection, you might be wondering, just how long am I infectious? And when is it safe for me to step out and socialize again without risking getting others sick?

The answer depends on whom you ask.

According to guidance from the Centers for Disease Control and Prevention, you can exit isolation five days after a positive test or the start of symptoms, so long as your symptoms are improving and you keep wearing a mask around others an additional five days.

However, this guidance comes with caveats: It's largely based on data from prior variants, and it was shaped by practical considerations – namely, how to make sure workplaces had enough staff to keep functioning at a time when omicron infections were racing across the country.

Meanwhile, emerging science suggests that, with the omicron variant, as many as half of the people infected will still be potentially infectious on day five – and some may be for a few days beyond.

"What we know based on the data so far is we can't reliably use five days as a way to exit isolation," says Dr. Peter Chin-Hong, a professor of medicine and infectious disease specialist at the University of California, San Francisco.

So how can you know if you are ready to rejoin the world — without potentially infecting others? Here are some science-based criteria that can help you figure it out.

How much time has passed?

At least three studies have found that people infected with omicron still have virus levels high enough to be contagious more than five days after their symptoms began.

Researchers looked at data from the National Basketball Association's extensive COVID testing program. Their study found that around 50% of people infected with omicron were still testing positive on a PCR test on day five. And compared with people infected with delta, there was a lot more variability in how long it took people with omicron to hit their peak viral load.

"For some people with omicron, it happens very, very fast. They turn positive and then they hit their peak very quickly. For others, it takes many days" – up to eight or even 10 days after turning positive, says the study's senior author, Dr. Yonatan Grad, an associate professor of immunology and infectious diseases at the Harvard T.H. Chan School of Public Health.

Another small study from Japan found that virus levels were highest on days three through six, and then gradually started to drop off. After 10 days, nobody in the study had infectious virus detectable on a PCR test.

And a third study, of 260 vaccinated health care workers in Chicago, found that overall, 43% were testing positive on rapid antigen tests five to 10 days after infection with omicron – even though they felt well enough to return to work. The rates of positivity "were higher on day six and seven and lower on days nine and 10," says study co-author Dr. Emily Landon of the University of Chicago Medicine.

Given all these findings so far, Landon says if you can't test again to exit isolation, waiting "eight days is a lot safer than six days." Just keep wearing your mask though day 10, she says.

After 10 days, you can consider yourself good to go, says Chin-Hong. He says multiple studies have shown that "there's very little, if any, transmission after day 10, regardless of the variant." There's one notable exception to this rule of thumb: If you're immunocompromised, you should wait 20 days to exit isolation, because research prior to omicron has shown that these patients tend to shed virus longer.

What symptoms do I still have, if any?

With prior variants, data suggested that people were most infectious just before and in the day after their symptoms developed, says Chin-Hong. That influenced the CDC's five-day guideline for exiting isolation.

But the relationship between symptoms and infectivity isn't as well understood with omicron, says Landon – in part because so many people are now vaccinated. Because vaccination primes the immune system, "it doesn't take so long to rev up, so that it can react to even small amounts of virus in your body," she says. So symptoms can be a sort of early-warning siren of an infection, even if you're not yet contagious.

On the flipside, you can still be infectious even if you're feeling better. In Landon's study, health care workers were still testing positive even though they felt well enough to return to work. "We were really surprised," says Landon. "They didn't seem sick" – yet many still had virus levels likely to be infectious.

And you can continue to experience symptoms even after you are no longer infectious "because your immune system is still active," says Chin-Hong.

So how should symptoms guide you? First of all, if you've got a fever, that's a red flag, says Chin-Hong – "because the type of immune response you get that results in a fever is usually because there's a ton of virus floating around."

If you're fever-free but you are still feeling sick, "that's not a great sign" – keep isolating for as much of that 10 day period as possible, and keep masking around others, says Landon.

But if you are feeling better and 10 days have passed since the start of your symptoms or your first positive test, consider yourself good to go. One caveat: If you are planning to see someone vulnerable, it's best to wait until your symptoms have all resolved.

Can I use testing to decide when to come out of isolation?

First, make sure you understand which kind of test you are taking. A PCR test is very accurate at the start of an infection because it can detect and amplify even trace amounts of virus DNA. But a PCR is not the right choice to figure out when you are no longer infectious, because of its sensitivity, Grad explains.

"There are some people who have little blips of being PCR positive for weeks, or in some cases even months, after an infection" – even though they're no longer contagious, Grad says.

A better bet is to use a rapid antigen test, because they're "positive when your viral load is high," corresponding to levels when people are likely to be infectious, says Landon. So if you're negative on a rapid test and you don't have any symptoms, consider yourself in the clear, says Chin-Hong.

What if 10 days have passed and you're still testing positive on a rapid test? "That definitely happens, and we don't have a good answer" as to why, says Landon. One thing to look at is how faint the positive line is on the rapid test, she says, because research has shown that the darker or more intense the line is and the more quickly it shows up, the more virus is present in your nose. So if you're past day 10, you feel better and you're not immunocompromised, and the rapid test line "isn't very dark or it's taking longer to turn positive each day, you're probably safe to be out in the world," she says.

But if you're going to be around vulnerable people, such as someone who's had a recent organ transplant, is elderly or is otherwise at risk of severe disease with COVID, then even a very faint positive line should make you think hard about being in contact with these folks, Landon says.

And remember, when you're out in public, you never know when someone you interact with in the grocery store could be immunocompromised or highly vulnerable. So if you have any doubt of your infectiousness, wear a high-quality mask in public out of consideration for those people. [Copyright 2022 NPR]