It is not always clear how long a person is contagious because, like a lot of things with COVID-19, the exact timeline depends on many factors, said Dr. Stuart Ray, a professor of medicine and infectious diseases at the Johns Hopkins University School of Medicine in Baltimore.
But, Ray said, the conventional wisdom is that you are contagious and must isolate for five full days after your symptoms begin — with your first day of symptoms counting as day zero.
But keep in mind that you aren’t in the clear after five days.
“It’s often said then that you should wear a mask after that to try and protect others because it’s hard to be certain how long you’re infectious,” Ray said.
“That period often lasts up to 10 days,” he added — and once again, your first day of symptoms counts as day zero.
Long story short, you are likely contagious for about 10 days after symptoms begin. You should isolate for the first five days and wear a mask on at least days six through 10.
The phase when you’re most contagious starts about 48 hours before you test positive and ends five days after your symptoms begin, according to Dr. Neha Vyas, a family medicine doctor at Cleveland Clinic in Ohio. She called this the “period of maximal contagiousness.”
So, you’ll want to be extra careful at this stage — though it’s hard to know if you’re sick before you have symptoms, which makes those first 48 hours really tricky.
Meanwhile, the amount of time between infection and symptoms has gotten shorter and shorter as COVID-19 mutates, which means omicron subvariants like XBB — currently the dominant strain in the U.S. — can spread faster.
If you’re exposed to someone who tests positive for COVID-19, you can test yourself even before you have symptoms. Or, if you recently attended a crowded indoor event, you can take a test a few days later. Beyond that, there isn’t really a way to know you’re infected before you start showing symptoms.
And in the later period of your illness, remember that you can still spread COVID-19, which is why it’s important to wear a mask until at least the 10-day mark.
Anyone whose symptoms persist past day 10 and who continues to test positive can likely pass the virus to others. If that’s you, keep wearing a mask and avoiding indoor spaces and events, Ray said.
“If you are immunocompromised or you had a really [severe] COVID infection ... then you could be contagious still for 20 days” after symptoms begin, added Vyas.
Long periods of contagiousness like this are rare, she stressed. But if you fall into either of those two categories, talk to your doctor for further guidance.
It’s not uncommon for someone to test positive on a lab test for weeks after a COVID-19 infection, “but it would be very unusual for someone to test positive for weeks on an antigen test,” Ray said.
Antigen tests are the type that you may have picked up from the pharmacy or received from the government.
Ray added that a positive antigen test is correlated with a virus’s ability to grow and infect. So if you have a positive antigen test, you are likely contagious.
And that works the other way around, too.
“We generally say if your symptoms are completely resolved and you have a negative test, you’re unlikely to be infectious,” Ray said.
If you’re past the 10-day mark and no longer symptomatic, but you’re feeling anxious about potentially spreading the virus to a loved one, there are things you can do.
“You can take two COVID tests 48 hours apart,” Vyas said. “If they’re both negative, you can [be] fairly certain that you’re not contagious anymore.”
She added that most people won’t need to do this as long as they follow the 10-day guidance. But if you’re nervous about passing on the virus, this is a good tactic.
“If possible, a contagious individual should use a separate bedroom and bathroom, especially during this five-day period [after symptoms begin],” said Dr. Ali Khan, the chief medical officer at Oak Street Health.
When that isn’t possible, wear a well-fitting mask — ideally an N95 or KN95 — around other people in your home.
Khan added that an infected person should have their own tableware and sheets, and that they should avoid high-touch items.
“Don’t forget to wash your hands frequently,” Khan said — and this goes for people who are not infected, too.
Lastly, to protect both yourself and your loved ones, make sure you’re up to date on your COVID-19 boosters.
“It’s definitely not too late to get COVID-19 and flu shots, as they will still curb severe symptoms, even if you do contract illness,” Khan said.
Omicron XBB.1.5: Latest COVID-19 variant most contagious yet
The latest COVID-19 variant to gain a foothold in America is called XBB.1.5, which has rapidly started to crowd out other competing variants.
XBB.1.5 is the first recombinant COVID-19 variant expected to become dominant in the United States, according to the viral surveillance company Helix. This variant is called "recombinant" because it was created by two Omicron subvariants merging through evolution.
The new strain also took two evolutionary steps instead of just one, gaining a mutation for immune evasion, as well as an unsuppressed ability to bind to and infect human cells, Helix said in its report.
These rapid-fire mutations -- as well as the battle for supremacy that Omicron variants are waging in human bodies -- are relatively unprecedented, said Dr. Greg Poland, director of the Mayo Clinic's Vaccine Research Group.
"There was not one virologist I know of, including myself, not one of us thought we would see anything other than Delta subvariants," Poland said. "Instead, out of nowhere came Omicron. None of us expected that.
"And now what Omicron is demonstrating is something I have never really seen in my career before called convergent evolution, which means that what we're seeing is a swarm of Omicron subvariants battling one another for dominance," Poland added.
Omicron XBB.1.5 is the dominant strain across the United States, accounting for 43% of cases, according to the U.S. Centers for Disease Control and Prevention.
However, the variant is raging even harder in some parts of the nation.
In the Northeast, where XBB.1.5 is suspected to have first emerged, the variant makes up at least 82% of new cases, the CDC said.
"In my neck of the woods, it's probably four out of five at least," said Dr. Aaron Glatt, chief of infectious disease at Mount Sinai South Nassau in Oceanside, N.Y.
Is it more transmissible?
The World Health Organization has called XBB.1.5 the most transmissible COVID-19 variant ever, said Dr. Bhavna Lall, a clinical assistant professor of adult medicine at the University of Houston College of Medicine.
"It's spreading pretty rapidly and it's the most contagious Omicron variant yet," Lall said. "It's the most contagious COVID-19 variant that we've had so far."
The XBB.1 variants are dramatically better at evading the neutralizing antibodies in humans that protect against initial infection, according to a new study published Wednesday in the New England Journal of Medicine.
XBB.1 variants escape neutralizing antibodies 17 times more effectively than the BA.5 variant -- and that's if someone's gotten a booster dose of the standard mRNA vaccine, a Beth Israel Deaconess Medical Center team led by renowned virologist Dr. Dan Barouch reported.
The variant only "broke out" in December and became dominant in mid-January, so it's too early to tell whether it causes more severe illness.
At this point, "the good news is it doesn't seem to be more dangerous" than prior Omicron variants, Glatt said. "I don't think it causes more complications than previous strains."
Do vaccines and boosters still protect you?
The fact that you are much more likely to be infected by XBB.1.5 does not mean that COVID-19 vaccines and boosters are ineffective.
That's because the vaccines do more than just spur your body to produce neutralizing antibodies. They also teach T-cells -- the memory cells of the immune system -- what the COVID-19 virus looks like, so the body can mount a defense following infection.
"Given the mutations that XBB has evolved, it is not surprising that it is able to escape neutralizing antibodies and cause infections despite their presence," said Dr. Amesh Adalja, a senior scholar with the Johns Hopkins Center for Health Security in Baltimore.
"However, protection against severe disease remains intact in most people because immunity is not just a function of neutralizing antibodies, but a more complex phenomenon with multiple arms," Adalja added.
The CDC presented data on a conference call last week supporting that contention, said Dr. William Schaffner, medical director for the National Foundation for Infectious Diseases.
"If you've never been vaccinated, and there are such people, you are 17 times more at risk for hospitalization and severe disease than if you had been completely vaccinated and boosted," Schaffner said. "If you are vaccinated but have not yet received the bivalent booster, you're two and a half times at increased risk of being hospitalized."
Based on that, experts still recommend that people get vaccinated and boosted, particularly those in high-risk groups.
"Especially in the elderly and the immunocompromised, this would be a great way to boost your immunity so you have some protection against severe disease," Lall said.
Another piece of good news is that experts believe the handful of COVID-19 antivirals that have been developed will continue to work against XBB.1.5.
"Paxlovid works fine for it. Remdesivir works fine for it. Molnupiravir possibly works for it. So, there are treatments," Glatt said.
Importantly, people need to start taking antiviral drugs within five days of developing symptoms, Lall said. She added that COVID-19 drugs and vaccines remain free in the United States.
Unfortunately, monoclonal antibodies no longer work.
That development "unfortunately has led to the removal of the emergency use authorization for some of the monoclonal antibodies," Glatt said. "Essentially right now there are no monoclonal antibodies that work against XBB.1.5."
Are more COVID-19 variants coming?
Don't be surprised if even more COVID-19 variants rear their heads in months and years to come, experts say.
"I would be shocked if they weren't more variants," Glatt said. "They're going to occur. And the advantage that a new variant has over the previous strain may or may not make it better or worse for human beings."
Until Next time: Stay Safe, Stay Healthy and be Careful out in the World.
James A Vito, D.M.D.