(Reuters) - The BA.2 sub-variant of Omicron was estimated to be 23.1% of the coronavirus variants circulating in the United States as of March 12, the U.S. Centers for Disease Control and Prevention (CDC) said on Tuesday.
Scientists are tracking a rise in cases caused by BA.2, which is spreading rapidly in parts of Asia and Europe.
According to the CDC's data, the sub-variant now makes up 39% of total cases in regions including New Jersey, New York, Puerto Rico and Virgin Islands.
In states such as Connecticut, Maine, Massachusetts, New Hampshire, Vermont and Rhode Island, the sub-variant now makes up about 38.6% of total cases.
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U.S. daily cases have started to decline in recent weeks after touching record levels in January, with the CDC dramatically easing its COVID-19 guidelines for masks, including in schools.
Initial data for the BA.2 sub-variant, which has begun to replace Omicron's more common BA.1 variant, shows no significant difference in disease severity, the World Health Organization said last month.
Other Omicron sub-variants that have been circulating since December, called BA.1.1 and B.1.1.529, now make up for around 66.1% and 10.8% of circulating variants, respectively.
For the week ending March 5, CDC estimates that BA.2 made up 13.7% of circulating variants, revised up from 11.6%, according to a CDC model that estimates proportions of circulating variants. The agency has revised its estimates in the past as it gets more data.
(Reporting by Bhanvi Satija in Bengaluru; Editing by Amy Caren Daniel)