The CDC's Nowcast data tracker, which displays COVID-19 estimates and projections for two-week periods, reflected that the KP.3.1.1 variant accounted for 57.2% of positive infections, followed by XEC at 10.7% in the two weeks starting on Sept. 29 and ending on Oct. 12.

Now, as we in the northern hemisphere move into autumn and winter, there is concern about two new variants. The first one is known as KP.3 and its sub-variant KP.3.1.1. The second is XEC, a "recombinant" variant which is related to KP.

“It might start becoming the top circulating lineage,” Rajnaranayam said, predicting XEC will take the rest of October and early November to gradually outcompete KP.3.1.1 in the United States, becoming the dominant lineage over the winter 2024/25 season.

New COVID strain XEC is a recombinant strain of two variants in the Omicron family: KS.1.1 and KP.3.3. The hybrid strain was first reported in Berlin in late June but has spread across Europe, North America and Asia, with Germany, France, the Netherlands and Denmark leading the charge.