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What to Know About XBB.1.5, the Latest COVID Variant

The omicron strain is spreading quickly in many areas of the U.S. and around the world

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Public health experts are keeping a close eye on a new coronavirus strain that’s quickly taking over. It’s known as XBB.1.5, and the latest data from the Centers for Disease Control and Prevention (CDC) shows the omicron subvariant is behind an estimated 30 percent of COVID-19 cases in the U.S., up from 4 percent a few weeks ago. In the Northeast, it’s causing about 70 percent of infections. Here’s what we know so far about XBB.1.5 and the impact it could have this winter.

It’s more transmissible

Like its relatives, this omicron spinoff is highly transmissible, says John O’Horo, M.D., an infectious disease expert at Mayo Clinic, meaning it spreads quickly and easily from person to person. And in many areas of the country, it’s outcompeting other prominent omicron strains like BQ.1 and BA.5, “which usually implies that it has some sort of transmission advantage [over the others],” O’Horo says.

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World Health Organization (WHO) officials confirmed on Jan. 4 that XBB.1.5 is, indeed, “the most transmissible subvariant that has been detected yet,” thanks to certain mutations that allow the virus to easily bind to cells and replicate. Cases of COVID-19 caused by XBB.1.5, a hybrid of two omicron BA.2 sublineages, are also on the rise in Europe, and the subvariant has been detected in 29 countries and counting.

It may be better able to bypass immunity

What’s more, XBB.1.5 seems to be even better at evading antibody protection from vaccines or a prior infection, O’Horo says. That’s not to say the vaccines can’t stand up to XBB.1.5. “There are parts of the immune system other than antibodies, and it still seems that there is a reduction in severity of illness and reduction in risk of hospitalization and death,” O’Horo says about the shots. 

Studies to determine just how well the vaccines can neutralize XBB.1.5 are ongoing. In the meantime, doctors and health officials are urging everyone who is eligible to get the updated bivalent booster, which targets some of the more recently circulating omicron strains. “The new bivalent shot is your best protection against both infection and serious illness [from XBB.1.5],” White House COVID-19 Response Coordinator Ashish Jha, M.D., said in a tweet. As of Jan. 4, nearly 40 percent of adults 65 and older have received the booster.

Tests and treatments? So far, so good

It’s still unclear if XBB.1.5 causes more severe illness — there’s no indication that it does, WHO officials have said — but what we do know is that the three antiviral medications used to treat COVID-19 “seem to have a high degree of efficacy” against the subvariant, O’Horo says. “So we’re hardly without treatment options for it.” (Monoclonal antibodies are no longer being used to treat COVID-19 caused by the latest omicron strains, which have essentially rendered the medications ineffective.)


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The evidence so far also points to our COVID-19 tests working “just fine” with XBB.1.5 in the mix, Jha said. If you experience symptoms that align with COVID — cough, sore throat and fatigue are among the more common signs — test right away, Jha advises. And if you’re positive for the virus, talk to your doctor immediately about treatment options that can help keep an infection from progressing into severe illness. 

Now is not the time to abandon preventive measures

The situation with XBB.1.5 is no doubt one to watch. But there’s no need for panic, says Pavitra Roychoudhury, a virus expert at the University of Washington and a research associate in the Vaccine and Infectious Disease Division at the Fred Hutchinson Cancer Center.

“It’s definitely good to be aware that there’s this highly transmissible variant out there, and that it’s only adding to the existing circulation of other respiratory viruses that we’ve been hearing about,” Roychoudhury says. The U.S. has already been hit hard with a wave of flu and RSV (respiratory syncytial virus) this fall and winter. 

In addition to staying up to date with your vaccines, Roychoudhury’s advice is to keep your risk top of mind. If you’re going to be around others in an indoor setting, consider wearing a mask, which, she says, “still works against all [COVID] variants and multiple respiratory viruses.” 

Also, avoid poorly ventilated spaces and stay away from others if you’re feeling sick, to help break the chain of transmission if you do have COVID. “The more this virus circulates, the more opportunities it will have to change,” WHO’s Maria Van Kerkhove said.

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