The Omicron BA.5 subvariant is no longer the dominant cause of Covid-19 infections in the United States, according to estimates released Friday by the US Centers for Disease Control and Prevention.
Instead, a host of new sublineages – offshoots of BA.2, BA.4 and BA.5 – are now responsible for the majority of new infections in this country. Dr. Peter Hotez, director of the Center for Vaccine Development at Texas Children’s Hospital, calls these many new lineages “Scrabble variants” because they contain letters like X and Q that get high scores in the game.
The new variants descend 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 slip past our immunity against the virus.
The gaggle of new variants have been gaining ground 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, have been growing especially fast. At the beginning of October, each one accounted for about 1% of new infections in the United States, but they have been roughly doubling in prevalence each week. Together, they now account for more than 1 in 4 new Covid-19 infections nationwide, according to CDC data.
BQ.1 is causing about 14% of new infections; BQ.1.1. is causing 13% of new infections. BA.4.6 is causing another 10%. BF.7 accounts for 7.5% of newly diagnosed Covid-19. A slew of other new variants accounts for smaller pieces of the Covid-19 pie.
These variants are not evenly distributed across the US. BQ.1.1 is now causing about 1 in 5 new Covid-19 infections in the Northeast, where cases and hospitalizations are rising. But that strain is causing just 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 skirt immunity from vaccines and past infections. This makes them more likely to lead to breakthrough infections and reinfections.
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In a statement released Friday, the World Health Organization’s Technical Advisory Group on SARS-CoV-2 Virus Evolution said the most mutated families of the rising subvariants – XBB and BQ.1 – aren’t different enough from Omicron to be considered separate variants of concern.
XBB was detected in the United States in September, but it is not causing a significant number of cases in this country. It is particularly widespread in Singapore, where it is now the dominant circulating strain.
“The two sublineages remain part of Omicron, which continues to be a variant of concern,” the group said in a statement.