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.
BA.5 and BA.4 are, like BA.2.12.1, more transmissible, but have the added advantage of reportedly being more able to reinfect those who’ve already had Covid.
“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.