BA.2's prevalence in US falls for 3rd week

The omicron subvariant BA.2 accounts for a fewer proportion of new COVID-19 cases in the U.S. as the prevalence of another omicron sublineage — BA.2.12.1 — grows, according to the CDC's latest variant proportion estimates

BA.2 accounted for 56 percent of new cases for the week ending May 7, down from about 74 percent for the week ending April 23. Meanwhile, BA.2.12.1 is gaining more of a foothold, accounting for nearly 43 percent of new cases for the week ending May 7. The CDC estimates show the newer sublineage accounted for just under 23 percent for the week ending April 23. 

BA.2.12.1 is estimated to have a 25 percent growth advantage over BA.2, which is already more transmissible than the original omicron strain. CDC Director Rochelle Walensky, MD, said there haven't been indications it's tied to more severe disease. 

“Epidemiologically, it doesn’t appear as if we’re seeing more severe disease in places that are having more cases,” she said during an April 26 news conference. "So we are not anticipating more severe disease from some of these subvariants, but we are actively studying it.

"Importantly, we continue to believe that those who are vaccinated, and especially those who are boosted, continue to have strong protection against severe disease, even from BA.2.12.1," Dr. Walensky said. 

The shift comes as cases rise nationwide. The daily average for new cases on May 9 was 73,056, marking a 49 percent increase across the last 14 days, federal data collected by The New York Times shows.

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