Omicron 'sister variants' gain traction in US

BA.4 and BA.5 — "sister variants" of the original omicron strain — are gaining prevalence in the U.S. and now account for about 1 in 5 confirmed COVID-19 cases nationwide, CDC data shows.

BA.5 accounted for 13.3 percent of all COVID-19 cases in the week ending June 11, while BA.4 accounted for 8.3 percent, according to the agency's latest variant proportion estimates. The prevalence of these subvariants, first identified in South Africa this winter, has been rising steadily since early May.

The omicron subvariant BA.2.12.1 is still the nation's dominant strain — having overtaken BA.2 last month — and accounted for 64.2 percent of all COVID-19 cases in the week ending June 11.

"Given the data we've seen so far, I'd expect BA.4 and BA.5 would continue to replace BA.2.12.1," Tom Inglesby, MD, an epidemiologist and director of the Johns Hopkins Center for Health Security at the Johns Hopkins Bloomberg School of Public Health in Baltimore, told The Hill.

Early research suggests BA.4 and BA.5 aren't more contagious than other omicron subvariants, but they may be better at evading immunity from a past infection, according to The Hill. There is also no evidence they cause more severe disease. 


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