Third dose of anti covid vaccine, currently available data on vaccine efficacy do not support the need for a new booster for the general population. This is the conclusion of a review conducted by an international group of scientists, including experts from the World Health Organization WHO and the American drug agency Fda, published in ‘The Lancet’. The authors explain that, even against the Delta variant of Sars-CoV-2, the effectiveness of Covid-19 vaccines is such as to make booster vaccine doses “inappropriate” for everyone.
Researchers analyzed evidence from randomized controlled trials and observational studies published in peer-reviewed journals and pre-print platforms. On average, Covid vaccination shows 95% effectiveness against severe disease caused by both the Delta variant and the Alpha variant of the pandemic coronavirus, as well as more than 80% effectiveness in protecting against any infection associated with these variants. .
For all vaccine types and against all variants considered, the effectiveness of immunization is greater against severe disease than for mild forms. And although compared to the protection provided against serious disease, vaccines appear less effective in avoiding asymptomatic infections or transmission of the contagion, “even in populations with high vaccination coverage – the scientists specify – the unvaccinated minority is still the main factor of transmission, as well as being itself at greater risk of serious illness “.
“Taken together – says Ana-Maria Henao-Restrepo of WHO, lead author of the review – the studies currently available do not provide credible evidence of a substantial decline in protection against serious disease, which is the primary goal of vaccination” anti-Covid.
“The limited supply of these vaccines – observes the researcher – will save most of the lives if it is made available to people who are most at risk of serious forms of” Covid-19 “and have not yet received any vaccines. of a ‘booster’ could produce a certain benefit “, this” will not outweigh the advantages of providing initial protection to the unvaccinated – warns the expert – If vaccines were now distributed where they are needed most, they could accelerate the end of the pandemic, inhibiting the further evolution of the variants “.
The authors of the publication note that, “even if the levels of antibodies in vaccinated people decline over time, this does not necessarily lead to a reduction in the effectiveness of vaccines against severe disease.” This may be due to the fact that protection against severe disease occurs not only through antibody responses, but also thanks to other, more lasting forms of immunity (cell-mediated immunity). So, if additional doses are given, “it will be necessary to identify specific circumstances in which the benefits outweigh the risks“, the researchers warn.
Also if in the future new variants of Sars-CoV-2 emerge that could escape the current anti-Covid vaccines, according to the authors of the review it is very likely that they do so from strains that have already become widely prevalent. Therefore, the scientists still remark, “the effectiveness of booster vaccines developed specifically to counter possible new variants could be greater and more lasting, compared to that of vaccine boosters made using current products”.
Moreover, the researchers note, “a similar strategy is also adopted for anti-influenza vaccines: each annual vaccine is based on the most recent circulating strains, increasing the probability that the injection remains effective even in the event of further evolution” of the virus.
“The Covid-19 vaccines available today are safe, effective and save lives – says Soumya Swaminathan, WHO chief scientist, co-author of the review – Although the idea of further reducing the number of Covid cases by boosting immunity in already vaccinated people is tempting, any decision to do so should be based on highlight and consider the benefits and risks for individuals and society. These decisions – he insists – should be based on solid evidence and international scientific discussions “.