How Protected Am I Against the Covid Variant JN.1?

Over the last few years, the general assumption has been that a Covid infection — or vaccination — is likely to buy you a few months of protection. But any time we get a new variant that is especially adept at evading the immune system, like JN.1, that assumption gets thrown into question.

JN.1 currently accounts for about 93 percent of cases nationwide, according to data from the Centers for Disease Control and Prevention. It’s unusual for a single variant to make up almost all cases, but JN.1’s dominance gives us a unique window into the risk of reinfection for many people.

If you had Covid when cases rose over the summer, or if you received the updated vaccine in the fall, here’s what to know.

If I had Covid during the summer, how much protection do I have now?

You may be vulnerable to reinfection if you were infected over the summer, when earlier variants drove an uptick in cases.

That doesn’t mean you’ll definitely get sick. “You should have some protection, for sure,” said Aubree Gordon, an infectious disease epidemiologist at the University of Michigan. Immunity is an individual cocktail that stems from how many times you’ve been previously infected, your vaccination history, underlying medical conditions and more. People who are 65 and older, immunocompromised or who have underlying medical conditions are generally at greater risk of reinfection, said Fikadu Tafesse, a virologist at Oregon Health & Science University.

If a person is exposed to the same variant or a very similar one in the months that follow a bout of Covid, their body is often equipped to recognize and combat it before it can cause an infection. Scientists disagree on exactly how long that protection lasts, but estimates range from around two to six months.

But JN.1 has “many more mutations than we’re used to seeing,” said Dr. Marc Sala, co-director of the Northwestern Medicine Comprehensive Covid-19 Center in Chicago. That’s why people who were recently infected with another variant, even one that was previously dominant, may get infected again.

What if I got the booster in the fall?

A C.D.C. report published this month showed that people who received the updated vaccines that came out in the fall had 54 percent more protection against a symptomatic case of Covid than people who did not get the shot. The vaccines were formulated to target XBB.1.5, an earlier variant, but they still offer some protection against JN.1, said Ruth Link-Gelles, the lead author on the study. “They’re all very closely related,” she said.

But even though a vaccinated person is less likely to develop symptomatic infections, that person is still not completely protected from the virus.

That said, there is still “quite a lot of benefit” from the updated vaccine, he said. Notably, vaccines reduce the risk of severe disease and hospitalization, he said. Experts urged people who are 65 or older or who are immunocompromised, in particular, to get the shot. As of late January, only about 12 percent of eligible children and 22 percent of adults had received an updated vaccine, according to the C.D.C.

For many people, the more immunity you’ve built up — through infection, vaccination or both — the milder your symptoms will probably be, Dr. Gordon said. Some people may become infected with JN.1 and experience such mild symptoms that they don’t even realize they are ill, she said. People with compromised immune systems or underlying medical conditions, though, may still have strong symptoms.

And those who do get infected with JN.1 will likely find themselves well protected for as long as it remains the dominant variant. Right now, it isn’t showing any signs of slowing down.