"FLiRT" COVID variants are now more than a third of U.S. cases. Scientists share what we know about them so far.

More than a third of COVID-19 cases in the U.S. are now estimated to be from a new, fast-growing member of a group of so-called "FLiRT" variants, nicknamed for their small but distinctive changes relative to the JN.1 strain. JN.1 was the variant behind this past winter wave of infections.

The largest among them, called KP.2 by scientists, has quickly multiplied in recent weeks to become the now-dominant new COVID-19 strain. 

According to the Centers for Disease Control and Prevention's every-other-week variant estimates, KP.2 and another strain with the same FLiRT mutations, called KP.1.1, together make up a projected 35.3% of infections this week. This is up from 7.1% a month ago.