The Omicron BA.5 subvariant is no longer the dominant cause of Covid-19 infections in the United States, according to grades published Friday by the US Centers for Disease Control and Prevention.
Instead, multiple new sublineages—branches of BA.2, BA.4, and BA.5—are now responsible for most new infections in this country. Dr. Peter Hotez, director of the Vaccine Development Center at Texas Children’s Hospital, calls these many new lines “variants of Scrabble” because they contain letters like X and Q that score high in the game.
The new variants come from slightly different branches of the Omicron family tree, but they have evolved to share some of the same changes in their genomes that help them get past our immunity to the virus.
The set of new variants is gaining strength against BA.5, which has dominated Covid-19 infections in the United States since July. BA.5 now accounts for 49.6% of new infections in this country.
Two variants, BQ.1 and BQ.1.1, grew particularly fast. In early October, they each accounted for about 1% of new infections in the United States, but their prevalence is doubling roughly every week. Together, they now account for more than 1 in 4 new Covid-19 infections nationwide, according to CDC data.
BQ.1 causes about 14% of new infections; BQ.1.1. causes 13% of new infections. BA.4.6 causes another 10%. BF.7 accounts for 7.5% of newly diagnosed Covid-19. A host of other new options represent smaller pieces of the Covid-19 pie.
These variants are not evenly distributed across the US. BQ.1.1 now causes about 1 in 5 new Covid-19 infections in the Northeast, where cases and hospitalizations are rising. But this strain causes only 3% of new Covid-19 infections in the Pacific Northwest.
These variants are slightly different from each other, but they all carry some of the same key mutations that help them overcome immunity from vaccines and past infections. This makes them more likely to lead to breakthrough infections and reinfections.
In a statement released on Friday, the World Health Organization’s Technical Advisory Group on the Evolution of the SARS-CoV-2 Virus said that the most mutated families of the growing subvariants – XBB and BQ.1 – are not sufficiently different from Omicron to be considered as separate variants of concern.
XBB was discovered in the United States in September but does not cause a significant number of cases in that country. It is particularly widespread in Singapore, where it is now the dominant circulating strain.
“The two sub-lines remain part of Omicron, which continues to be an option of concern,” the group said in a statement.
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