For most of this year, the JN.1 variant of the coronavirus accounted for an overwhelming majority of COVID-19 cases. But now an offshoot variant called KP.2 is taking off. The variant, which made up just 1% of cases in the United States in mid-March, now makes up more than one-quarter.

KP.2 belongs to a subset of COVID variants that scientists have cheekily nicknamed “FLiRT,” drawn from the letters in the names of their mutations. They are descendants of JN.1, and KP.2 is “very, very close” to JN.1, said Dr. David Ho, a virus expert at Columbia University. But Ho has conducted early lab tests in cells that suggest that slight differences in KP.2’s spike protein might make it better at evading our immune defenses and slightly more infectious than JN.1.

While cases currently don’t appear to be on the rise, researchers and physicians are closely watching whether the variant will drive a summer surge.

What is current spread of COVID?

Experts said it would take several weeks to see whether KP.2 might lead to a rise in COVID cases and noted that we have only a limited understanding of how the virus is spreading. The Centers for Disease Control and Prevention no longer tracks case counts, and doctors said fewer people were using COVID tests.

But what we do know is reassuring: Despite the shift in variants, CDC data suggests there are only “minimal” levels of the virus circulating in wastewater nationally, and emergency department visits and hospitalizations fell between early March and late April.

Protection from past infections, vaccines

Experts said that even if you had JN.1, you may still get reinfected with KP.2 — particularly if it’s been several months or longer since your last bout of COVID.

KP.2 could infect even people who got the most updated vaccine, Ho said, since that shot targets XBB.1.5, a variant that is notably different from JN.1 and its descendants. An early version of a paper released in April by researchers in Japan suggested that KP.2 might be more adept than JN.1 at infecting people who received the most recent COVID vaccine. (The research has not yet been peer-reviewed or published.) A spokesperson for the CDC said the agency was continuing to monitor how vaccines perform against KP.2.

People who are age 65 and older, pregnant or immunocompromised remain at higher risk of serious complications from COVID.

Doctors said the symptoms of both KP.2 and JN.1 — which still account for a considerable chunk of cases — are most likely similar to those seen with other variants. These include sore throat, runny nose, coughing, head and body aches, fever, congestion, fatigue and, in severe cases, shortness of breath. Fewer people lose their sense of taste and smell now than did at the start of the pandemic.