A group of experts from the US drug agency, the FDA, and the World Health Organization (WHO) has just concluded that there is no solid evidence that a third dose of vaccine is necessary for the general population.
Researchers have conducted a comprehensive review of clinical trials on the effectiveness of vaccines and observational analyzes of their performance in different countries.
The work, published in the medical journal The Lancet, shows that the efficacy of these drugs remains acceptable 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. However, more and more people have become infected with COVID, and have had to be hospitalized even after having two doses injected into their bodies, which implies that such protection does wear out after just a few months.
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. That is a different assessment from the one that was provided even before the vaccine was created, when so-called experts said the vaccine would prevent infection.
“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 Hainaut.
“Given the limited number of vaccines available, more lives will be saved if we give them to those who have a higher risk of covid, who are those who have not yet received a dose.”
“Although a third dose may provide some benefit, the benefits of immunizing the unvaccinated are much greater,” write the study authors. Following this advice “can accelerate the end of the pandemic, as it will prevent more variants of the coronavirus from evolving,” they add.
This assessment has been contested by medical doctors who find that using vaccines may cause the virus to mutate further and have the population face new strains whose infection ability is unknown.
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. Yet, people who have received both doses continue to be hospitalized with severe cases of COVID.
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. In fact, so called asymptomatic people do not even need to be vaccinated, since their bodies are able to deal with the virus on their own.
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 their 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.
“We must be very cautious with the matter of the third dose,” experts conclude. “One of the things that this work 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 emphasizes.