An expert review published in medical journal, The Lancet, has recommended that booster doses for the general population are not appropriate at this stage of the COVID-19 pandemic, weighing in on the global debate that calls for caution in administering booster doses.

An international group of scientists, including those at the World Health Organisation and the U.S. Food and Drug Administration agency, concluded that even for the Delta variant, vaccine efficacy against severe COVID is so high that at this stage that boosters would not be appropriate and not required. The review summarises the currently available evidence from studies published in peer-reviewed journals and pre-print servers.

“The message that boosting might soon be needed, if not justified by robust data and analysis, could adversely affect confidence in vaccines and undermine messaging about the value of primary vaccination,” the paper states.

Further, it goes on to explain: There could be risks if boosters are widely introduced too soon, or too frequently, especially with vaccines that can have immune-mediated side-effects. If unnecessary boosting causes significant adverse reactions, there could be implications for vaccine acceptance that go beyond COVID-19 vaccines.

A consistent finding from the observational studies is that vaccines remain highly effective against severe disease, including that from all the main viral variants, a release states. Averaging the results reported from the observational studies, vaccination had 95% efficacy against severe disease both from the Delta variant and from the Alpha variant, and over 80% efficacy at protecting against any infection from these variants, the release adds.

The authors note that even if antibody levels in vaccinated individuals wane over time, it did not necessarily mean reduction in the efficacy of vaccines against severe disease. This could be because protection against severe disease is mediated not only by antibody responses, which might be relatively short lived for some vaccines, but also by long-lived memory responses and cell-mediated immunity.

The ability of vaccines to elicit an antibody response against current variants indicates that these variants have not yet evolved to the point at which they are likely to escape the memory immune response induced by the vaccines. Even if new variants that can escape the current vaccines do evolve, they are most likely to do so from strains that have already become widely prevalent, and it makes sense to use boosters that have been specifically made to attack potential new variants.

“The limited supply of these vaccines will save the most lives if made available to people who are at appreciable risk of serious disease and have not yet received any vaccine. Even if some gain can ultimately be obtained from boosting, it will not outweigh the benefits of providing initial protection to the unvaccinated. If vaccines are deployed where they would do the most good, they could hasten the end of the pandemic by inhibiting further evolution of variants,” says lead author Ana-Maria Henao-Restrepo of the WHO.

“Although the idea of further reducing the number of COVID-19 cases by enhancing immunity in vaccinated people is appealing, any decision to do so should be evidence-based and consider the benefits and risks for individuals and society. These high-stakes decisions should be based on robust evidence and international scientific discussion,” added Soumya Swaminathan, WHO Chief Scientist, and co author.