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JN.1 COVID Variant Sweeps U.S.

The fast-growing coronavirus strain is behind the biggest share of cases in the country

spinner image blue and red COVID-19 mutation illustrations on a black background
ChakisAtelier / Getty Images

A new crop of coronavirus variants is sweeping the U.S. at a time when many Americans are returning from holiday travel. And health officials are keeping a close eye on one variant in particular: the fast-growing JN.1 strain, which the World Health Organization has classified as a “variant of interest” due to its “rapidly increasing spread.” 

JN.1 now accounts for nearly half of COVID-19 cases in the U.S., up from about 7.5 percent a few weeks ago. In some areas of the country, it makes up the majority of coronavirus infections, according to data from the Centers for Disease Control and Prevention (CDC). 

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Its continued growth suggests that JN.1, a close relative of the highly mutated BA.2.86, is either more transmissible or better than other circulating variants at evading our immune systems, the CDC said in a Dec. 22 report. Still, the health agency says, it’s “too early to know whether or to what extent” JN.1 will cause an increase in coronavirus infections or hospitalizations.

“We know this virus is changing, and it has changed again,” CDC Director Mandy Cohen, M.D., said in a recent briefing. “You want to get that updated COVID vaccine for this exact reason.”

Don't count on last year's vaccine

Similar to how the flu shot is updated each year to target new strains, the COVID-19 vaccine was recently revamped to more closely match the variants that are currently circulating. So far, public health experts say it’s remained effective against JN.1 and other variants in the mix.

If you’re relying on last year’s COVID-19 shot to protect you from this year’s variants, “that’s like having a vaccine that was for an apple, and now we're seeing oranges,” says Jodie Guest, a professor and senior vice chair in the department of epidemiology at Emory University’s Rollins School of Public Health. “So we want to make sure you're getting the most recent type of vaccine, so we'll be able to protect you the best.”

But uptake of the new COVID-19 vaccine has been low since the shot was approved in September — about 18.5 percent of adults have received it, CDC estimates show — leaving many Americans without optimal protection as we head into winter.

All this while COVID-19 hospitalizations are increasing in the U.S., climbing about 10.5 percent in recent weeks. Deaths from the virus are also rising, federal data shows.

There’s no indication that JN.1 causes more severe infections, the CDC says. Rather, this trend is “quite expected” this time of year, says William Schaffner, M.D., an infectious disease specialist and professor of medicine at Vanderbilt University School of Medicine in Nashville. 

“Each winter in the past that COVID has been with us, we’ve had increases,” he says, hand-in-hand with spikes in other respiratory illnesses. Data from the CDC shows that in addition to COVID-19, activity is picking up for flu and RSV throughout the country. In particular, several states in the South are reporting high or very high respiratory illness activity levels.

spinner image united states map showing the level of respiratory illness by state on january second twenty twenty four the highest levels are showing in new mexico and the southeast states louisiana alabama mississippi arkansas tennessee and georgia
Respiratory illness activity levels in the U.S. Data as of Dec. 21, 2023.
Courtesy CDC

How to stay safe this holiday season

The concern with JN.1, Guest says, is that it appears to spread more easily from person to person.  

The good news is there are several things you can do to help keep yourself protected, most of which are very familiar at this point in the pandemic.


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If you’ve put away your mask, consider taking it back out in certain situations — say, if you’re on a crowded airplane or in a busy store. “[Masks] can be situational; you don't have to have them on all the time,” Guest says.

Find COVID-19 Vaccines in Your State

AARP's 53 state and territory COVID-19 vaccine guides can help you find vaccines near you and provide the latest answers to common questions about costs, eligibility and availability.

Wash your hands often and stay home when you’re not feeling well so you don’t get others sick. Testing before gathering is another measure that can help keep COVID from spreading. Plus, if you test positive for COVID-19, there are effective treatments, such as Paxlovid, that can help keep you out of the hospital. (Out of tests? You can get four shipped to you for free from

If you haven’t had your COVID vaccine this year, it’s not too late. “But don’t linger,” Schaffner says. The same advice goes for the flu shot and the new RSV vaccine, which was approved for adults 60 and older, since those illnesses tend to peak around the same time.

In addition to lowering your risk of getting seriously sick, staying up to date with the COVID-19 vaccine can also prevent the emergence of other variants, including any future strains that may not respond as well to our vaccines, tests and treatments. That’s because the more a virus circulates in a population, the more opportunities it has to mutate.

“Every new case is a place for a variant to happen,” Guest says. “And so if we are protecting ourselves and others from COVID-19, we are helping prevent new variants from popping up.”

Editor's note: This story, first published Dec. 14, 2023, was updated with new information on respiratory illness activity levels.

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