The review by experts, including those from the World Health Organization (WHO) and the US Food and Drug Administration (FDA), summarized the currently available evidence from randomized controlled trials and observational studies published in peer-reviewed journals. peer-to-peer and prepress servers.
Results reported from observational studies, on average, show that vaccination was 95 percent effective against severe disease from both Delta and Alpha variants, and more than 80 percent effective in protecting against any infection with these variants.
The authors found that across all vaccine types and variants, the vaccine is more effective against severe disease than against mild disease.
Although vaccines are less effective against asymptomatic disease or transmission than against severe disease, even in populations with high vaccination coverage, the unvaccinated minority continues to be the main driver of transmission, in addition to running the highest risk of contracting a serious illness, they said.
“Taken together, the currently available studies do not provide credible evidence of a substantial decrease in protection against severe disease, which is the primary goal of vaccination,” said lead author Ana-Maria Henao-Restrepo of the WHO.
“The limited supply of these vaccines will save the most lives if it is made available to people who are at appreciable risk of serious diseases and have not yet received any vaccines,” Henao-Restrepo said.
The authors noted that even if some benefit may ultimately be obtained from the booster, it will not outweigh the benefits of providing initial protection to the unvaccinated.
If vaccines are implemented where they would be most beneficial, they could hasten the end of the pandemic by inhibiting further evolution of variants, they added.
The authors explained that even if antibody levels in vaccinated people decrease over time, this does not necessarily predict reductions in the effectiveness of vaccines against severe disease.
This could be because protection against serious disease is mediated not only by antibody responses, which may be of relatively short duration for some vaccines, but also by memory responses and cell-mediated immunity, which generally have a lifespan. longer, they said.
“The vaccines that are currently available are safe, effective and life-saving,” said study co-author Soumya. Swaminathan, WHO Chief Scientist.
“Although the idea of further reducing the number of COVID-19 cases by improving immunity in vaccinated people is attractive, any decision in this regard must be based on evidence and consider the benefits and risks for people and society,” he added Swaminathan.
According to the review, if reinforcements are ultimately to be used, it will be necessary to identify specific circumstances where the benefits outweigh the risks.
The authors also noted that the ability of vaccines to elicit an antibody response against current variants indicates that these variants have not yet evolved to the point where they are likely to escape the vaccine-induced memory immune response.
Even if new variants are to evolve that can escape current vaccines, they are more likely to do so from strains that have already become widely prevalent, they said.
Therefore, the authors said, the effectiveness of boosters developed specifically to match possible newer variants could be greater and more durable than boosters using current vaccines.
A similar strategy is used for influenza vaccines, for which each annual vaccine is based on the most recent data on circulating strains, increasing the likelihood that the vaccine will remain effective even if there is a further evolution of the vaccine. strain, they added.