Data published this week by researchers at the Kirby Institute suggest updated bivalent boosters do offer big improvements over the original vaccines, even if they are not up against the exact target variant.
Using data from laboratory studies, the team concluded that updated boosters increase antibody responses by, on average, 1.5 times as much as the original vaccine. Against the variant they directly target, that rises to 1.75
The improvement from a bivalent vaccine is not nearly as significant as getting a booster at all,” says study co-author Dr Deborah Cromer.
Approving an updated vaccine using animal data may raise eyebrows – particularly given concerns raised by some groups about the speed of original vaccine approvals. But it has precedent. Australian regulators approve one version of the updated influenza vaccine every year using animal data.
“The regulatory agencies have essentially said because the process stays the same they do not require human data,” says Professor Kanta Subbarao, director of the WHO Collaborating Centre for Reference and Research on Influenza at the Doherty Institute.
That strategy allows vaccine-makers to follow quickly changing influenza strains. COVID-19 poses similar challenges.
“The advantage is clearly that it potentially allows regulators to provide much more rapid access for recent strain-optimised versions of existing vaccines,” says Jim Buttery, head of epidemiology and signal detection at Victoria’s vaccine safety service.
“The risks are clearly if there is an unanticipated change in the way the vaccine behaves in humans – safety, immunogenic, efficacy – it could undermine confidence.”
Indeed, scientists always caution animal studies are no substitute for human data. Influenza vaccines that work well in animals sometimes struggle to be effective in humans.
“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 naive.”
But given the speed the virus is changing at, the Kirby’s Cromer is sceptical our vaccines could ever truly catch up to it.
“The idea that we are specifically going to be able to match the circulating strain with a vaccine seems highly unlikely to me anyway. And our work suggests that boosting with any variant booster is still effective,” she says.