Using data from laboratory studies, the team concluded that the updated boosters increase antibody responses by, on average, 1.5 times more than the original vaccine. Against the variation they target directly, which goes up to 1.75 Getting better from a bivalent vaccine is not as important as getting a booster,” says study co-author Dr. Deborah Cromer. Approving an updated vaccine using animal data may be a cause for concern — especially given the concerns expressed by some groups about the speed of initial vaccine approvals. But it has a precedent. Australian regulators approve one version of the updated flu vaccine each year using animal data. “The regulators basically said because the process remains the same they don’t require human data,” says Professor Kanta Subbarao, director of the WHO Collaborating Center for Influenza Reporting and Research at the Doherty Institute. This strategy allows vaccine makers to keep up with rapidly changing flu strains. COVID-19 poses similar challenges. “The benefit is clearly that it potentially allows regulators to provide much quicker access to recent strain-optimized versions of existing vaccines,” says Jim Buttery, head of epidemiology and signal detection at Victoria’s vaccine safety agency. A doctor gives a dose of the Moderna vaccine to a motorist at a drive-by vaccination station in an IKEA parking lot in Berlin, GermanyCredit: Carsten Koall/Getty Images “The risks are clear if there is an unanticipated change in how the vaccine behaves in humans – safety, immunogenicity, efficacy – it could undermine confidence.” Indeed, scientists always caution that animal studies are no substitute for human data. Flu vaccines that work well in animals sometimes struggle to be effective in humans. Loading “It’s very difficult to extrapolate from humans to animals with influenza because humans have had a lifetime of exposure [to the virus], says Subbarao. “Animals are usually immunologically naïve.” But given the speed at which the virus is changing, Kirby’s Cromer is skeptical that our vaccines could ever really cover it. “The idea that we’ll specifically be able to match the circulating strain with a vaccine seems very unlikely to me anyway. And our work suggests that boosting with any enhancer variant is still effective,” he says.