New COVID variant makes up 21% of US cases: What to know

JN.1 is now the fastest-growing COVID-19 variant in the U.S., accounting for around 21% of cases, data from the CDC shows.

The strain is closely related to BA.2.86, which first caught experts' attention over the summer because of its large number of mutations in the spike protein. JN.1 has a single additional change in its spike protein, the L455S mutation, which experts say has some immune-evasion properties worth keeping an eye on.

"The continued growth of JN.1 suggests that it is either more transmissible or better at evading our immune systems," the CDC said in a recent update about the variant. "At this time, there is no evidence that JN.1 presents an increased risk to public health relative to other currently circulating variants." 

The strain has grown rapidly, with estimates showing it accounted for less than 4% of cases in mid-November. In its variant proportion tracker, the CDC noted that projections for an emerging lineage with a high growth rate "may have a higher degree of uncertainty." For JN.1, the CDC estimated the prevalence could be between 15% and 29% for the week ending Dec. 9. 

Initial data has indicated the new COVID-19 shots, which were made to target XBB variants, offer protection against BA.2.86, so experts anticipate similar protection levels against JN.1. 

JN.1's growth comes as COVID-19 activity, including hospitalizations, rises across the country. New admissions were up nearly 18% for the week ending Dec. 4, marking the fourth straight week of increase. The CDC said it is not clear to what extent JN.1 may be driving the increases. 

Based on data currently available, the CDC estimates its prevalence is highest at nearly 32% in HHS Region 2, which includes New Jersey, New York, Puerto Rico and the Virgin Islands. 


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