A little over a month after the more transmissible BA.2.12.1 Omicron subvariant became officially dominant in the U.S. on May 24, two sister subvariants of Omicron have quickly eclipsed BA.2.12.1 across the country.
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“We now report findings from a systematic antigenic analysis of these surging Omicron subvariants,” says a paper published last month to the BioRxiv preprint server. “BA.2.12.1 is only modestly (1.8-fold) more resistant to sera from vaccinated and boosted individuals than BA.2. On the other hand, BA.4/5 is substantially (4.2-fold) more resistant and thus more likely to lead to vaccine breakthrough infections.”
While BA.2.12.1 accounts for 42% of new cases this week, Centers for Disease Control and Prevention data shows that’s down from about 53% the week before. BA.5 and BA.4 by contrast have grown their shares from 25% and 12%, respectively, last week to about 37% and 16% this week. That means together the two variants which first emerged in South Africa earlier this year have jumped to a 55% share of all new cases in the last week.
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