An international group of scientists, including specialists from the World Health Organization (WHO) and the US Food and Drug Administration Agency (FDA), affirms that the efficacy of covid-19 vaccine is so high that booster dose for the general population are not appropriate at this stage of the pandemic, even for the delta variant.
The review, published in The Lancet, summarizes the currently available evidence from randomized controlled trials and observational studies conducted: vaccines remain highly effective against severe disease, including all major viral variants.
Thus, vaccination had a 95% efficacy against severe disease of both the delta variant and the alpha variant, and more of the 80% effective in protecting against any infection of these variants. In all types of vaccines and variants, the efficacy is greater against severe disease than against mild.
Although there may be some benefit to the booster, it will not outweigh the benefits of providing initial protection to the unvaccinated. If vaccines are deployed where they can do the most, they could hasten the end of the pandemic by inhibiting the evolution of variants
Ana-María Henao-Restrepo (WHO)
“Although vaccines are less effective against asymptomatic infection or transmission than against severe disease – even in populations with high vaccination coverage – the unvaccinated minority continues to be the main driver of contagion, in addition to being the one that runs the greatest risk of developing a serious episode ”, explain the authors.
According Ana-Maria Henao-Restrepo, lead author and WHO expert, “the available studies do not provide credible evidence of diminishing protection against severe disease, which is the primary goal of vaccination. The limited supply of these doses will save the greatest number of lives if it is made available to people who are at appreciable risk of having a serious case and who have not yet received one ”.
“Even if there is ultimately some benefit to be gained from the booster, it will not outweigh the benefits of providing initial protection to the unvaccinated. If vaccines are deployed where they can do the most good, they could hasten the end of the pandemic by inhibiting the evolution of variants, “he adds.
Booster dose, better with updated formulas
The researchers note that, although the levels of antibodies in vaccinated individuals decrease over time, this does not necessarily predict reduced efficacy against severe disease. This could be because protection is mediated not only by antibody responses, which can be relatively short for some vaccines, but also by memory responses and cell-mediated immunity, which are generally longer lasting.
For the authors, if reinforcements are finally used, it will be necessary to identify the specific circumstances in which the benefits outweigh the risks. “Increasing success in immunizing large populations will inevitably lead to an increase in the number of people vaccinated and thus to a higher proportion of success stories, especially if such vaccination leads to behavioral changes.”
The idea of further reducing the number of COVID-19 cases by increasing the immunity of vaccinated people is attractive, but any decision about it must be based on solid evidence and evidence.
Furthermore, the ability of vaccines to elicit an antibody response against current variants indicates that these varieties have not yet evolved sufficiently to escape the dose-induced memory immune response. Even if they do, the efficacy of boosters specifically developed to accommodate potential new variants could be greater and more durable than boosters with current vaccines.
A similar strategy is used for flu shots, for which each year the formula is based on the most current data on circulating strains, which increases the probability that the medication will remain effective even if there is a greater evolution of the strains.
“Currently available vaccines are safe, effective and save lives. Although the idea of further reducing the number of covid-19 cases by increasing the immunity of vaccinated people is attractive, any decision in this regard must be based on evidence and consider the benefits and risks for individuals and society, ”he concludes. Soumya Swaminathan, co-author and chief scientist at WHO.
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