The updated COVID-19 vaccines' effectiveness between BA.5 and XBB subvariants are similar, according to CDC data published Jan. 25.
In a study of COVID-19 infections among immunocompromised adults between Dec. 1 and Jan. 13, when XBB.1.5 was prevalent, the CDC found an overall 49 percent vaccine efficacy in people ages 18-49. When BA.5 was dominant, the boosters showed a 52 percent efficacy in the same age group.
"Findings from this study suggest that bivalent booster doses are continuing to provide additional protection against symptomatic infection for at least the first 3 months after vaccination in persons who had previously received 2, 3, or 4 monovalent vaccine doses, which supports recommendations to continue to increase bivalent booster coverage," the researchers wrote in conclusion.
The FDA authorized the bivalent shots Sept. 1, and they were engineered to target omicron subvariants BA.4 and BA.5, with the latter dominating COVID-19 cases in summer 2022. Since then, multiple subvariants have cropped up; one of them, XBB.1.5, accounts for nearly 1 in 2 COVID-19 infections.