What to know about the omicron variant and subvariant BA.2

A more transmissible subvariant, BA.2, has become the dominant strain in the United States as the omicron surge has waned. Those most at risk are the unvaccinated and older than 75

The BA.2 “stealth” omicron variant is expected to soon become the dominant strain. Here is what you need to know about a possible new wave of infections. (Video: Brian Monroe, John Farrell/The Washington Post)
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After emerging in November, the omicron variant spread rapidly across the globe because of mutations that allowed it to evade some of the immunity produced by vaccinations and previous infections. In midwinter, tens of millions of people in the United States, many of them fully vaccinated and boosted, were infected by omicron.

Now, a subvariant called BA.2, which has many mutations not seen in omicron, is posing a new threat and accounting for a swiftly growing share of cases in the United States, as it propels sharp case increases in Europe and Asia. Preliminary research suggests BA.2 is at least 30 percent more transmissible than omicron.

The Centers for Disease Control and Prevention estimated that, as of March 19, BA.2 accounted for 35 percent of new infections. The genomics company Helix, analyzing more current data, put its own estimate at 70 percent. Both estimates show a steady rise toward dominance of the subvariant.

The rise in BA.2 cases comes as federal health authorities have relaxed certain recommendations. On Feb. 25, the CDC updated its mask guidelines, which no longer recommend masking for most people in indoor public spaces in counties with low to medium levels of covid-19 community transmission and hospitalizations. Most of America is now classified at those lower levels. However, other prevention strategies, such as vaccinations, are still recommended.