BA.5 Omicron Is Winning The Covid Variant Battle In The U.S., Especially In The Southwest

The BA.5 Omicron variant, first identified in South Africa on February 26, now seems to have an edge in the competition for dominance across the United States.

Three Covid variants are currently on the rise as the country experiences a summer surge in cases. All are members of the Omicron family. While BA.5 still only accounts for 7.6% of cases in the country, according to data released by the Centers for Disease Control and Prevention today it is clearly making bigger week-by-week gains than any other variant. Similar trends have repeatedly led to other Omicron strains becoming dominant in the U.S.

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The current dominant variant BA.2.12.1, which only achieved that status two weeks ago, currently accounts for 62.2% of new positive cases in the U.S. where a variant was identified.

Last week, BA.2.12.1 accounted for 59% of variants identified. That’s a 5.4% rise in the past week. The week before BA.2.12.1 saw a roughly 7% increase overall.

But BA.5 rose from 4.2% to 7.6% in the past week, an 85% rise in the past week. That’s even more than the 74% increase the South African variant saw the week before, an acceleration.

Sister lineage BA.4, first identified in South Africa in January, rose from 3.3% to 5.4% of all variants sequenced in the past week. That’s a considerable 64% increase, but not on par with BA.5. See chart below.

. - Credit: CDC
. - Credit: CDC

CDC

The South African variants have increased their shares even more rapidly in the Southwest, specifically in Texas and New Mexico, where together the already account for close of one-quarter of all new cases, at 22.2%. See map below.

In those two states, BA.5 was identified in 13.2% of new cases analyzed for variants this week. That’s at 71% rise from the 7.7% share BA.5 held just last week. Compare that to BA.2.12.1, which rose from 52% of all new cases to 53% this week netting only about a 2% rise and its clear which variant has the advantage going forward.

. - Credit: CDC
. - Credit: CDC

CDC

So what gives BA.5 and BA.4 an advantage? While BA.2.12.1 gained the upper hand by being more transmissible than BA.2 before it, the two newer variants are said to be making inroads at least in part because of their abilities to reinfect.

“We now report findings from a systematic antigenic analysis of these surging Omicron subvariants,” says a recent analysis published 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.”

If true, that means the new variants have a much larger population that they can potentially access, given that previous variants like BA.2.12.1 are producing far fewer breakthrough infections.

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