Covid-19 levels are about the lowest they’ve ever been in the United States, but another new crop of virus variants once again threatens to disrupt the downward trend as the country heads into summer.

KP.2 — one of the so-called FLiRT variants — has overtaken JN.1 to become the dominant coronavirus variant in the United States, according to data from the US Centers for Disease Control and Prevention. Data through May 11 shows that it’s responsible for more than a quarter of cases in the country, which is nearly twice as many as JN.1. A related variant, KP.1.1, has caused about 7% of cases, CDC data shows.