A group of experts from the US drug agency and the World Health Organization has just concluded that there is no solid evidence that a third dose of vaccine is necessary for the general population.
Researchers have done a comprehensive review of clinical trials on the effectiveness of vaccines and observational analyzes of how vaccines work in different countries.
His analysis, published today in the medical journal The Lancet, shows that the efficacy of vaccines remains very high against all variants of the coronavirus, including delta. “The body of evidence accumulated so far appears to show that there is no need for a third dose in the general population, as its protection against severe disease is still high,” the authors write.
Observational studies show that injections are on average 95% effective against severe covid and 80% against infection, regardless of severity. And these data, experts recall, are valid for all known variants. It is true, they add, that the effectiveness of vaccines is greater against severe covid than against milder symptoms.
“The studies published so far do not provide credible evidence that protection against severe covid, which is the main objective of vaccines, is decreasing,” highlight the authors of the analysis, led by the head of WHO research, Ana María Henao, along with experts from the US Federal Drug Agency (FDA), among others. “Given the limited number of vaccines available, more lives will be saved if we give them to those who are at higher risk of covid, which are those who have not yet received a dose.
It is true, experts add, that the effectiveness of vaccines is greater against severe covid than against milder symptoms
Although a third dose may provide some advantage, the benefits of immunizing the unvaccinated are much greater ”, write the authors of the study. Following this advice “can accelerate the end of the pandemic, as it will prevent more variants of the coronavirus from evolving,” they add.
The researchers recall an argument that most immunity experts make. The fact that some studies show that there is a drop in the level of antibodies – proteins of the immune system capable of blocking the entry of SARS-CoV-2 into cells – does not mean that the efficacy of vaccines is falling. The fact that there is a reduction in the protection of the vaccines against moderate or asymptomatic covid does not mean that there will be a failure of the protection against severe covid. The possible explanation is that not only antibodies come into play in protecting against severe disease, but also memory cells of the immune system, the study notes.
Those responsible for the article say that it is possible that there are groups that do need that third dose, especially the immunosuppressed. They also reflect on the future. If new variants of SARS-CoV-2 emerge, they will probably be descended from the existing ones. None of them have been shown to completely circumvent the immune system. In his opinion, the most reasonable thing would be that if a third dose is approved, it is a new version of the vaccine specially designed against the dominant versions of the pathogen, such as delta. It is the same, they emphasize, that is done with the flu vaccine every year. Both Pfizer and Moderna are conducting clinical trials of new delta variant vaccines.
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“We must be very cautious with the issue of the third dose,” warns Marcos López, president of the Spanish Society of Immunology. “One of the things that this study highlights is that more studies are needed on the need for the third dose. It is an issue that still needs to be seriously analyzed before approving it, as we have no proof that the vaccine is failing, ”he highlights.
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