New data Tuesday from the Centers for Disease Control and Prevention show omicron’s more transmissible BA.2 subvariant now accounts for more than a third of the virus circulating in the U.S. but is not yet driving a surge in cases here as it has overseas. The CDC data show that as of March 19, BA.2 — often referred to as “stealth omicron” — accounted for 34.9% of genetically sequenced samples across the U.S., up from 22.3% as of March 12 and 12.6% on March 5. In the Northeast, BA.2 accounts for as much as 55.4% of the virus, and in Western states including California, 41.3%. Dr. George Rutherf...

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