A subvariant of omicron known as BA.2 is now the dominant strain in the United States, according to new data from the Centers for Disease Control and Prevention (CDC).
The variant has been steadily rising in proportion because of its increased transmissibility compared to the original omicron strain, and it represented 54.9 percent of new cases for the week ending March 26, according to CDC data. That is up from about 27 percent two weeks earlier.
The BA.2 subvariant is thought to be about 30 percent more transmissible than the original BA.1 omicron strain, which itself was already more contagious than earlier versions of the virus.
Importantly, though, experts say there is no evidence that BA.2 causes more severe disease than the original omicron strain or that it evades the protection from vaccines to a greater degree.
The subvariant may cause some increase in cases after weeks of steady declines that have led to a relative lull in the virus. But it is unclear how sharp the increase will be, and people who are vaccinated and boosted are still well-protected against severe disease.
The Food and Drug Administration on Tuesday authorized a fourth COVID-19 vaccine shot for people 50 and older, which could further help protect the most vulnerable from the subvariant.
“CDC says the BA.2 subvariant of Omicron is now dominant in the US,” tweeted Leana Wen, a public health professor at George Washington University. “Reminder that while this appears to be even more contagious than the original Omicron, it is not more virulent than previous strains, and existing vaccines still protect well against severe disease.”
CDC Director Rochelle Walensky said last week that her agency was monitoring the subvariant, particularly in the Northeast, where it has been concentrated so far.
“Over the past week, we have seen a small increase in reported COVID-19 cases in New York state and New York City, and some increases in people in the hospital with COVID-19 in New England, specifically where the BA.2 variant has been reaching levels above 50 percent,” she said.
“This small increase in cases in the Northeast is something that we are closely watching as we look for any indication of an increase in severe disease from COVID-19 and track whether it represents any strain on our hospitals. We have not yet seen this so far.”