Scientific evidence to date on COVID-19 vaccine efficacy does not support boosters for general population

An expert review by a world group of scientists, including some at the WHO and FDA, concludes that, even for the delta variant, vaccine efficacy against severe COVID is so high that booster doses for the overall population aren’t appropriate at this stage within the pandemic.
The review, published within the Lancet, summarises the currently available evidence from randomised controlled trials and observational studies published in peer-reviewed journals and pre-print servers.

A consistent finding from the observational studies is that vaccines remain highly effective against severe disease, including that from all the most viral variants. 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. Across all vaccine types and variants, vaccine efficacy is bigger against severe disease than against mild disease.

Although vaccines are less effective against asymptomatic disease or against transmission than against severe disease, even in populations with high vaccination coverage the unvaccinated minority are still the main drivers of transmission, also as being themselves at the very best risk of great disease.

“Taken as an entire , the currently available studies don’t provide credible evidence of substantially declining protection against severe disease, which is that the primary goal of vaccination. The limited supply of those vaccines will save the foremost lives if made available to people that are at appreciable risk of great disease and haven’t yet received any vaccine. albeit some gain can ultimately be obtained from boosting, it’ll not outweigh the advantages of providing initial protection to the unvaccinated. If vaccines are deployed where they might do the foremost good, they might hasten the top of the pandemic by inhibiting further evolution of variants,” says lead author Dr Ana-Maria Henao-Restrepo, WHO.

The authors note that albeit levels of antibodies in vaccinated individuals wane over time, this doesn’t necessarily predict reductions within the efficacy of vaccines against severe disease. this might be because protection against severe disease is mediated not only by antibody responses, which could be relatively short lived for a few vaccines, but also by heart responses and cell-mediated immunity, which are generally longer-lived. If boosters are ultimately to be used, there’ll be a requirement to spot specific circumstances where the advantages outweigh the risks.

Even with none loss of vaccine efficacy, however, increasing success in delivering vaccines to large populations will inevitably cause increasing numbers of vaccinated people, decreasing numbers of unvaccinated people, and hence an increasing proportion of all cases being breakthrough cases, especially if vaccination results in behavioural changes in vaccinees. But, the power of vaccines to elicit an antibody response against current variants indicates that these variants haven’t yet evolved to the purpose at which they’re likely to flee the memory immune reaction induced by the vaccines.

Even if new variants which will escape the present vaccines are getting to evolve, they’re presumably to try to to so from strains that have already become widely prevalent. Therefore, the effectiveness of boosters developed specifically to match potential newer variants might be greater and longer lived than boosters using current vaccines. an identical strategy is employed for influenza vaccines, that each annual vaccine is predicated on the foremost current data about circulating strains, increasing the likelihood that the vaccine will remain effective albeit there’s further strain evolution.

“The vaccines that are currently available are safe, effective, and save lives. Although the thought of further reducing the amount of COVID-19 cases by enhancing immunity in vaccinated people is appealing, any decision to try to to so should be evidence-based and consider the advantages and risks for people and society. These high-stakes decisions should be supported robust evidence and international scientific discussion,” adds co-author Dr Soumya Swaminathan, WHO Chief Scientist.

Philip R Krause, Thomas R Fleming, Richard Peto, Ira M Longini, J Peter Figueroa, Jonathan A C Sterne, Alejandro Cravioto, Helen Rees, Julian P T Higgins, Isabelle Boutron, Hongchao Pan, Marion F Gruber, Narendra Arora, Fatema Kazi, Rogerio Gaspar, Soumya Swaminathan, Michael J Ryan, Ana-Maria Henao-Restrepo. Considerations in boosting COVID-19 vaccine immune responses.
The Lancet, 2021. doi: 10.1016/S0140-6736(21)02046-8

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