Study: COVID boosters may be less than 20% effective after a few months

“Booster doses were found to restore the VE [vaccine effectiveness] to levels comparable to those acquired soon after administration of the second dose; however, a fast decline of booster VE against Omicron was observed, with less than 20% VE against infection and less than 25% VE against symptomatic disease at 9 months from the booster administration,” the authors wrote in the paper released Wednesday.

It’s a crucial question to understand, given that boosters widely became available about 9 months ago in the United States, and that a new surge is now happening with the BA.5 variant of omicron — which appears to be better at reinfecting people than any past strain of the virus.

Overall, the researchers found that nine months after administration, two doses of a vaccine were less than 5% effective at stopping a symptomatic omicron infection, and three doses were no more than about 22% effective.