9 big questions about Omicron explained

As scientists learn what makes Omicron different from other versions of the SARS-CoV-2 virus, guidance about how to deal with the variant is changing fast. In the U.S., where Omicron is now the dominant variant, the Centers for Disease Control and Prevention have come under fire for their shifting guidelines, including a recently updated recommendation that halves the isolation period for people who test positive from 10 days to five.

What is the science behind the changing guidance, and how can people best protect themselves as Omicron spreads? Here’s what experts say you need to know.

Why did the CDC change its recommended isolation period? 

The short answer? Practicality, says Gregory Poland, a vaccinologist and internal medicine specialist at the Mayo Clinic in Rochester, Minnesota. Because Omicron spreads so easily, cases have skyrocketed to more than 540,000 per day for the past seven days. And if hundreds of thousands of people all must isolate for 10 days, it becomes challenging to staff and operate critical businesses, including hospitals.

“What do you do if you have 20 percent or more of your healthcare workforce not able to work because they test positive?” says Poland. “You see a rapid rise in death and complications for whoever is in the hospital, because there are an inadequate number of healthcare workers.”

But there is also solid science behind the change. Studies have measured the concentration of live (and therefore contagious) virus in the noses of infected people and how levels change over time. They show that a person’s ability to transmit the virus typically peaks between a day or two before symptoms begin and two to three days after, says Jill Weatherhead, an infectious disease expert at the Baylor College of Medicine in Houston. So five days after a positive test, the amount of virus an infected person sheds drops sharply.

The new guidelines are a tradeoff, adds Abraar Karan, an infectious diseases doctor at Stanford University in Palo Alto. “The benefit is that we avoid huge losses in labor capacity,” he says. “The cost is that we send people back when they could still be infectious, although potentially far less so than earlier in their disease course.”

So five days after I test positive, I’m free? 

Not exactly. The five-day recommendation only applies to people who are asymptomatic or whose symptoms are diminishing at that point.

A negative test around the five-day mark also doesn’t necessarily mean you’re in the clear, Karan says. “You could still be infectious, even if you test negative on an antigen test,” Karan says. “But you are likely less contagious than when your antigen was positive.”

People who are immunocompromised take longer to get rid of their infections, experts say, and should stay in isolation for up to 20 days. For people who have healthy immune systems and whose symptoms are declining, masking will reduce the risk of transmitting the virus after the fifth day. Even after five days of isolation, people should wear well-fitting, high-quality masks snugly over their mouths and noses.

“The idea with the updated guidance is that you're really covered during that peak time of contagiousness to protect from transmitting the virus,” Weatherhead says. “And in case you are a person that continues to shed virus after those five days, continuing to wear a mask will provide another layer of protection to prevent transmission.”

How do I count down the days in isolation?

To isolate properly and reduce risk, day zero begins when your first symptoms appear, even if you tested positive before symptoms started. Day one is the first full day after your symptoms begin. If you never get symptoms, day one is the first full day after your positive test.

Isolation only applies to people who have tested positive, according to the CDC. This means staying away from other people, even other household members, preferably in a “sick room” or area with its own bathroom.

If you find out you’ve been exposed to someone who tested positive, the CDC recommends that you quarantine. This also means staying away from others for a while, but the details depend on your vaccination status. If you have been boosted, if you have received your second Moderna shot within the last six months, your second Pfizer shot within the last five months, or if you have received the Johnson & Johnson vaccine within the last two months, you don’t need to quarantine, but you should wear a mask around other people for 10 days.

If you are unvaccinated or you are not within the recommended time windows for vaccines and boosters, the CDC recommends staying home for five days, then wearing a mask around other people for five more days. If you can’t quarantine, wear a mask for 10 days everywhere you go. Anyone who is a close contact of someone who tests positive should test on day five if possible. And if symptoms appear, get tested and stay home.

When will I stop testing positive? 

The answer depends on which type of test you get, among other factors.

PCR tests detect genetic material from the SARS-CoV-2 virus. In some people, genetic remnants can linger in the nose for weeks or even months after the virus is no longer able to cause infections, Weatherhead says. Poland has a colleague who tested positive 16 weeks after their infection began.

Rapid antigen tests, on the other hand, detect viral proteins that are produced by live, active viruses. Those types of tests are unlikely to stay positive after levels of the virus are too low to cause infection.

A positive test of either kind doesn’t reveal how contagious you are, Weatherhead points out. Even though it may be tempting to interpret a faint line on a rapid test as a decline in infectiousness, faintness could simply be a result of how much virus you managed to pick up with the swab. “You're getting a ‘yes or no’ answer, not a ‘how much’ answer,” she says.

Do rapid tests even detect Omicron? 

Available evidence suggests that yes, they do, Weatherhead says. Sensitivity might be slightly lower with the new variant, the FDA said in a statement in late December. Compared to PCR tests, rapid tests are less likely to detect infections in their earliest stages. But a U.K. Health Security Agency briefing analyzed the performance of rapid antigen tests at detecting Omicron, and it found no change in their performance with Omicron.

Will I start getting negative tests sooner if I’m vaccinated and boosted?

Theoretically yes, experts say. In a December 2021 study of people infected with several variants, including Delta and Alpha but not Omicron, researchers reported that vaccinated people with breakthrough cases cleared their infections in an average of 5.5 days. By contrast, unvaccinated people took 7.5 days to clear even though peak viral load was the same in both groups. Studies also show that fully vaccinated people are less likely to develop severe cases of COVID-19, including those who catch Omicron.

Vaccination “certainly reduces your risk of developing severe disease and requiring hospitalization, because the immune system [is] primed to reduce the viral burden,” Weatherhead says. “Whether that translates into how quickly you convert from a positive antigen test to a negative antigen test, I don't think we have that data yet.”

Do I need to have a negative test result to stop isolation?

Although many public health experts think it would be a good idea, the CDC is holding firm on its decision not to recommend a negative test before leaving isolation.

The best answer might depend on whether you are trying to make policy decisions or individual ones, Poland says. On a population level, it might make sense to require negative tests to prevent potentially infectious children from going to school, for example.

But in your personal life, Weatherhead says, what you choose to do depends on your own level of risk tolerance and the vulnerability of people around you. “If you're around people who are unvaccinated or who have underlying health conditions who are at high risk of disease, maybe it's better to take that test or wait the full 10 days beforehand,” she says.

If I test negative, do I still need to wear a mask?

If you're vaccinated, boosted, and healthy, you have dramatically lowered the chance that you will have severe disease, be hospitalized, or die, Poland says. But you have only moderately decreased the risk that you'll get infected with the Omicron variant. Given how transmissible the variant is, Poland recommends wearing a mask if you're gathering in an indoor setting with people not in your household.

Plenty of people can become infected without ever knowing it and pass the virus onward, Karan adds. Masking can slow transmission between people who may be infectious but are without symptoms.

Ultimately, people will need to consider their health conditions, risk tolerance, vaccination status, and COVID-19 levels in the community when making masking decisions, Weatherhead says. “In general, if everyone is fully vaccinated, asymptomatic and has a negative PCR test, the risk will be low and people do not universally need to wear a mask, particularly if gathering outdoors,” she says. People “who have underlying health conditions or are at high risk of progressing to severe disease if they become infected with SARS-CoV-2 may choose to continue to wear masks even around fully vaccinated groups.”

How will I know if I have Omicron? 

Around the U.S., Omicron now accounts for more than 95 percent of new cases, according to data released this week by the CDC which uses a national surveillance system to get a sampling of circulating variants. But Delta is still around, and at-home tests won’t tell you which variant you have.

For all the variants, “the best thing we can do is really identify what our risk tolerances [are] and to make sure that we're protecting others, especially during that highly contagious period of time,” Weatherhead says. “Outside of that, making sure you're vaccinated, wearing your mask, will provide that layered approach to reduce those risks of transmission.”