COVID vaccines are holding up against highly contagious XBB variant, CDC finds

COVID-19 vaccines and boosters continue to hold up well against the latest viral variant, the Centers for Disease Control and Prevention said Wednesday.

First seen in August, the omicron variant known as XBB and its subvariant XBB.1.5 have taken over in the U.S. this last month as the cause of more than half of COVID-19 infections.

The booster is targeted at both the initial SARS-CoV-2 virus and the BA.4/BA.5 variants, but BA.5 and its subvariants account for just about 2% of cases right now and BA.4 and the original virus are essentially gone.

Officials had argued that a "bivalent" booster — addressing two forms of the virus instead of one — would be more protective than the original "monovalent" vaccine as the virus continues to evolve.

The new study found that, despite the mismatch in variants, the booster remains protective against XBB.

"There is incremental or additional protection from getting the bivalent on top of those past monovalent doses," said Ruth Link-Gelles, the paper's first author, on Wednesday in a CDC call with media.

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About 50 million Americans have received the latest bivalent booster – about 15% of the population – compared with nearly 270 million who have had at least one dose of the original vaccine. There is no data to show whether the bivalent vaccine is more protective than a monovalent vaccine would have been, since everyone in the U.S. received the bivalent version.

Most people who haven't gotten the recent booster were last vaccinated more than a year ago so their protection against mild disease was expected to have faded, just as it fades after an infection.

The new study only looked at the chance of suffering relatively mild symptoms from a recent infection, not severe disease.

Other data the CDC plans to release later Wednesday shows that being vaccinated reduces the risk of death 13-fold compared to being unvaccinated, while being up-to-date on boosters provides a two-fold reduction in risk, officials said on the call.

Another study, which hasn't yet been peer-reviewed, suggests that protection against COVID-19 fades within about three months against XBB, faster than against other variants.

Contact Karen Weintraub at

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This article originally appeared on USA TODAY: COVID vaccines protect against omicron subvariant XBB, CDC finds