Sunday, June 20

The third dose of the covid vaccine will depend on what the variants change | Society


The answer to the question of whether the Spanish elderly will need a third dose of the coronavirus vaccine next year is now being written in the outskirts of Jakarta (capital of Indonesia, with more than 30 million inhabitants) or the Nile Delta (where almost 40 million people live). Also in the crowded parties of young people of the first world. It is these places, where the virus can circulate widely among groups of the population not yet immunized, which multiply the risk of new mutations arising that rearm the pathogen, experts warn. Changes that would force the population to be revaccinated to avoid a new wave of hospitalizations and deaths.

Africa González, professor of immunology at the Center for Biomedical Research (CINBIO) of the University of Vigo, states: “The so-called third dose will only be necessary in two cases. The first is the least likely and would occur if vaccinated people begin to suffer reinfections because their defenses are no longer effective against the virus as they have lost their immune memory. The second would be the appearance of a new strain greatly changed compared to the current variants that would make the vaccines stop being effective. But, strictly speaking, then we would no longer be talking about a third dose, but about a new vaccine, as happens every year with the flu ”.

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Ugur Sahin, one of the founders of BioNTech – the pharmaceutical company that devised the vaccine marketed by Pfizer – gave wings to the debate on April 27 by predicting that the third dose will be necessary “between nine months and a year after the first full schedule. ”. The reason would be the decrease in the antibodies generated by the body. 15 days ago, the CEO of Moderna, Stéphane Bancel, insisted on this idea in an interview awarded to the French newspaper Sunday Newspaper.

Both support their claims in studies carried out by both companies that point to the loss of immune memory in vaccinated people. A few studies that have not been published, leading experts to welcome the announcements with caution. Rafael Cantón, head of the microbiology service at the Ramón y Cajal Hospital (Madrid), states: The information we have does not point to the loss of efficacy of the body’s immune response. If the pharmaceutical companies have these studies, they should make them public ”.

In a press conference held on May 28, the spokesman for the European Medicines Agency (EMA) assured that with the “available data” the third dose will not be necessary since the immune response achieved with current vaccines is sufficient against to all known variants of the coronavirus.

A nurse prepares the Pfizer vaccine at the Son Espases Hospital in Palma de Mallorca in January.
A nurse prepares the Pfizer vaccine at the Son Espases Hospital in Palma de Mallorca in January.Isaac Buj / Europa Press

Experts recall that the immune system, one of the most complex in humans, defends itself against pathogens on several levels. Magda Campins, head of the preventive medicine service at the Hospital Vall d’Hebron (Barcelona), explains that “antibodies are one of them, but the fact that they decrease does not mean that the body is left without defenses. There is cellular immunity, with leukocytes capable of producing antibodies again if the virus tries to infect the person again even several years later ”.

This specialist also considers that, with the available evidence, there is currently no reason to think that the third dose will be necessary. “If the pharmaceutical companies have studies that say otherwise, they must present it to the regulatory agencies, which will study them and, where appropriate, will approve these new doses,” he adds.

Experts recall that it is common, for example, for the body to run out of antibodies to hepatitis B years after the vaccine, but that the cellular memory maintains the ability to produce them if necessary. “I think that if no new strains emerge, the third dose will not be necessary,” Africa González details. “The immune response will be sufficient. There are studies that reveal that people infected with the first SARS, in 2002, are still capable of producing effective antibodies ”.

This memory is effective even among older people, who tend to have a poorer immune response. Countries like France have started to apply the third dose in some profiles of patients, such as cancer patients, transplant patients and other immunosuppressed patients. Although this measure has been taken as a precaution, Magda Campins considers it “somewhat premature”. The underlying idea is the same: although some studies seem to indicate that they lose antibodies quickly, “this does not mean that they do not have the ability to produce them again.”

New mutations

If the prevailing opinion is that the immune response offered by current vaccines will be sufficient to contain all known variants, the debate is more open about the new mutations that may arise and that would revaccinate the population. In the opinion of Luis Enjuanes, director of the coronavirus laboratory of the National Center for Biotechnology (CNB-CSIC), it is an equation in which probabilities and, therefore, chance intervene, but if the virus continues for a long time to replicate trillions of times daily in hundreds of millions of infected people it is foreseeable that this will eventually happen,

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“From what we have seen now, the virus has a history of mutating quite a bit, almost like the flu virus,” explains Emjuanes. Each time it replicates, therefore, the virus undergoes three changes and this can greatly alter its infective and vaccine escape capabilities. I think it is very possible that every year or at most every two the vaccines will have to be adapted to the variants or strains that are circulating at that time ”.

Other experts, however, believe that “there is still time” to prevent the emergence of these strains if the world is able to rapidly produce and distribute enough vaccines to immunize the world’s population. With far fewer people susceptible to contracting the virus and most of them vaccinated, those who become infected will be very mild and with a low viral load. The virus, therefore, will have much less opportunity to continue mutating and “the pandemic will control itself,” says Africa González.

Pfizer vials in Paris in May.
Pfizer vials in Paris in May.MARTIN BUREAU / AFP

On May 20, the European Commission announced the acquisition of 900 million new doses of the Pfizer-BioNTech vaccine for delivery between the end of this year and 2023, with the option of doubling that amount. It is the way to be prepared for any future scenario, since the available technology would also allow adapting these vaccines to new variants or strains.

Some experts, however, fear that this operation is a new first step towards a strategy that has proven its limits. The race of rich countries to monopolize doses in this first phase of the pandemic has left large areas of the globe lagging behind in the vaccination campaign, they recall that it is no coincidence that new variants have emerged in areas with less coverage, such as India, South Africa and Brazil. The British (alpha according to the new nomenclature), on the other hand, predates the mass manufacture of the first vaccines.

The worst-case scenario would be an endless loop in which poor vaccination in some parts of the globe allows the emergence of new strains against which rich countries rush to get vaccinated first. Africa González concludes: “To avoid this, the best strategy is the global one and it is desirable that it be the World Health Organization that carries it out.”


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