Is a booster vaccine against Covid-19 important?

Mexico.- The new wave cases of covid-19 originated by Delta variant has led to study the need for apply booster doses in the population already vaccinated. Although it is very attractive to further reduce the number of Covid-19 cases by improving immunity in vaccinated people, from the point of view described by Philip Krause and his collaborators in an article in the Lancet magazine, any decision in this regard must be based in tests and consider the benefits and risks for people and society.

So far, everything seems to indicate that the reinforcements they are not strictly necessary for all.

Protection against severe covid-19

Despite the fact that various studies have yet to be properly evaluated and others undertaken, the available evidence seems to indicate that there is no reason to apply a booster in the general population, since current vaccines are highly effective against severe disease.

The boost hypothesis is based on the decrease in neutralizing antibodies in the blood over time, however, even though humoral immunity appears to decrease, they do not necessarily predict reductions in vaccine efficacy over time.

In sum, reductions in vaccine efficacy against mild disease do not necessarily predict reductions in (typically higher) efficacy against severe disease.

The authors explain that this effect may be due to the fact that protection against serious diseases depends not only on the response of antibodies, which can be of relatively short duration in some vaccines, but also on the responses of memory cells and the responses of long-term immunity.

Studies must follow

Although the benefits of vaccines have been shown to outweigh the risks when applied to the general population, it is necessary to wait for more studies looking at the long-term side effects that vaccines may have, and it is important to observe the reactions in those individuals who they receive different vaccines in their primary immunization or as a booster.

“If an unnecessary booster causes significant adverse reactions, there could be implications for vaccine acceptance that go beyond COVID-19 vaccines,” the authors mention, therefore investigations should continue.

The data

When to reinforce?

A booster may be appropriate for those who have not been adequately protected by first and full immunization: those who received less effective vaccines or those who are immunosuppressed for some reason.


It is not yet known whether immunosuppressed people would benefit more from an additional dose of the same vaccine than in the primary immunization or from a different vaccine that could complement the primary immune response in these individuals.

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Update vaccines

If the variants have evolved to the degree that they express new antigens and then the originally generated immune response no longer adequately protects against the new variants, another dose of the updated vaccine will be required (Krause et al., 2021).

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