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Omicron Subvariant Now Dominant in U.S.; FDA, CDC OK Second Booster for Adults Over 50

March 29, 2022

The Omicron subvariant called BA.2 is now the dominant COVID-19 strain in the United States, one week after more than half of all tested cases in New England were linked to the variant for the first time.

BA.2 represents 54.9 percent of new cases nationwide for the week ending March 26, up almost 27 percent from two weeks ago, according to new data released by the Centers for Disease Control and Prevention. BA.2 now accounts for 72.6 percent of cases in New England, up from 55.4 percent in the CDC’s last report.

“A virus is going to virus,” says Dr. Ulysses Wu, Hartford HealthCare’s System Director of Infection Disease and Chief Epidemiologist. “That’s what it’s going to do. Its job is to mutate. It’s job is to change.”

The BA.2 subvariant is about 30 percent more transmissible than the original Omicron (BA.1). So far, it has not caused more severe illness than the original Omicron. Vaccines, particularly with a booster dose, have also offered protection against the subvariant known as Stealth Omicron. Connecticut’s daily positivity rate March 29 was 3.65 percent, up from 3.07 percent the previous day.

“I think it’s going to cause an increase in numbers,” says Dr. Wu, “but I don’t think we’re going to have a spike or surge. I’m keeping my fingers crossed.”

Below: A Nowcast breakdown of COVID-19 variants in New England, designated Region 1 by the CDC. Use the dropdown menu to track variants in other regions:

On the same day the CDC released the new data, the Food and Drug Administration authorized a second booster dose of the Pfizer-BioNTech and Moderna vaccines for adults ages 50 and older. The additional dose is available to people at least four months after their first booster. The CDC later recommended the second booster for people “who wish to increase their individual protection.” It also approved a second dose of Johnson & Johnson’s vaccine for anyone who received the first dose at least four months ago.

Yet fewer than 50 percent of those eligible in the United States have received their first booster. Connecticut, with 50.8 percent boosted, is tied with Colorado as the 11th-most boosted state.

Moderna had asked the FDA to authorize a second booster for all adults. Pfizer’s request targeted adults 65 and older. But research shows protection from the first booster diminishes within a few months. CDC research found the effectiveness of both the Pfizer and Moderna vaccine against hospitalization dropped to 78 percent from 91 percent within two months of the initial booster. The study included December and January, when Omicron spread across the nation.