First came Omicron, then came its highly contagious subvariant, BA.2. That subvariant gave rise to its own subvariants, whose share of new cases in the US is growing. The coronavirus is constantly mutating. While some variants seem to vanish, others have kept driving large outbreaks. Experts say a new form, BA.2.12.1, is spreading rapidly and will likely in the next weeks become the dominant form of the virus in the US. There’s no indication yet that causes more severe disease.
In the week ending Saturday, BA.2.12.1 made up about 36% of all new cases in the US, according to estimates by the US CDC . That’s up from 26% of cases the week before, and 16% of infections during the second week in April. First detected by New York state health officials in April, BA.2.12.1 is spreading more rapidly than the first versions of the Omicron variant, which caused a huge surge in cases over the winter. This version descends from BA.2 and appears to have spread even more quickly, although the reasons are still under investigation. “Omicron was more transmissible than Delta, which was more transmissible than Alpha,” said Krista Queen, director of viral genomics at Louisiana State University. BA2.12.1 is building on that trend, she added.
Reports of new cases nationally have doubled in the past month as Omicron subvariants have spread, according to a NYT database. In the past two weeks, cases overall have increased by 50%. But reported cases are likely an undercount since access to at-home tests has increased. Still, virtually every reported infection is from an Omicron subvariant, and although BA.2 is still the dominant form, BA.2.12.1 is quickly gaining ground. Hospitalisations have risen more slowly — up 18% in two weeks — but those rates tend to trail. Deaths have decreased 17% in the past two weeks.