A few weeks after passing the covid infection, the body of a healthy person who has previously received the full vaccination is something of a virus killing machine. His deeper immune system was already primed to avoid severe disease in the vast majority of cases, and recent contact with the coronavirus serves as something of a booster dose that helps produce new antibodies. Virologists and immunologists consulted by EL PAÍS are surprised by the new vaccination strategy, published this week by the Ministry of Health, which indicates the booster dose in people over 40 years from four weeks after infection, always six months later of the last dose. “From the immunological point of view it does not make sense,” says Marcos López Hoyos, president of the Spanish Society of Immunology.
There are no studies that support this guideline: the omicron is so recent that there has not been time to do them. Until now, the vaccination strategy had always been based on scientific evidence. The experts from the Vaccine Report were more conservative than other countries in recommending the booster dose. They waited for all the data to support it, especially in the population under 60 years of age, whose risk of becoming seriously ill or dying is very low if they have received the full guideline. This third inoculation came even somewhat late, in the opinion of experts such as Harvard University professor Miguel Hernán, who believes that it would have been effective in reducing the impact of the sixth wave if it had started earlier.
In the booster dose for the recently infected, the strategy has not waited for scientific evidence. “We cannot find an explanation,” emphasizes López Hoyos, who assures that it can even generate “problems in the immune system” with such a short interval. “After vaccination, an omicron infection is like a new dose, but more complete, because we not only expose ourselves to a part of the virus, as with the injection, but to all its antigens. Weeks later the body has effective antibodies. Not by giving one and another dose to infinity without time spacing are we going to get better protection “, he adds.
Jaime Jesús Pérez, from the Spanish Society of Vaccination, defends the decision of Health: “The knowledge that we have is pointing towards taking into account the suffering of the disease as a possible reinforcement, but the uncertainty is there and the international context as well. In no country in Europe or the United States is infection taken as part of the pattern. In public health decisions, recommendations must be made that, causing the least harm, bring about the greatest benefit. If evidence is generated that this dose is not necessary, the strategies will probably change ”.
Pérez acknowledges that the deadline could be extended, but attributes the decision to optimizing logistics and standardizing the strategy with other countries: “We must bear in mind that the campaigns are underway. And if a person does not receive the booster dose, they may be prevented from entering some countries that require it regardless of having passed the disease.
Adolfo García-Sastre, director of the Institute for Global Health and Emerging Pathogens at Mount Sinai Hospital in New York, sees no reason to receive a booster injection so soon after the infection. “I would not put it on four weeks after being infected, since this exposure to the virus serves as a booster dose. I would wait a few months for a vaccine designed against the new variants. What I would do is continue giving this third dose to those who have not had the disease, “he reasons.
The vaccination strategy does not explain the reasons for this decision. It is the opposite that happens, for example, with other guidelines, or with the vaccination of children, for which the document sets out the scientific evidence, risks, benefits and reasons for implementing it. The Ministry of Health responds to this newspaper that the guideline has been the recommendation of the Vaccine Conference, the group of technicians that has designed the entire strategy. And he clarifies that the text says that it is “at least” four weeks, but that it can be spaced more. Jaime Jesús Pérez, for his part, points out that the communities have the power to extend the schedule: in Murcia, for example, they have decided to put it at eight weeks.
An “arbitrary” term
Federico Martinón, a vaccine advisor to the World Health Organization, thinks that imposing four weeks (or eight) is “arbitrary.” He conjectures several reasons on which the experts who advise Health have been able to base themselves: “The complete vaccination regimen requires three doses and not two in light of current knowledge. That is to say, we are talking about reinforcement, but in reality two doses do not arrive and the pattern is three, and if today a person were vaccinated from scratch, we would put all three ”. Furthermore, he continues, natural infection confers “more unpredictable” protection than vaccine-induced. “Perhaps that is why it has been decided to ignore the fact that you have previously exposed yourself or not, now that there are sufficient doses. Obviously, from an immunological point of view, there is no rush to vaccinate after infection, but some kind of arbitrariness must be established, and four weeks is arbitrary, as it could be eight or four months, since we are not sure of how long this protection lasts and can vary depending on the person ”, he adds.
The four weeks after overcoming the infection would be for Martinón rather a public health strategy for logistical reasons, since it is not possible to make a tailored guideline for each citizen. “The most debatable point is whether, after omicron, the third dose with a vaccine with the original composition (based on the Wuhan variant) makes sense. That’s where we could say: ‘Well, since there is no rush, it was better to run out of time and put the third dose with a new generation one.’ And, once again, we must insist that we have to vaccinate those who need it most, wherever they are with the vaccines that we have. The benefits of a third dose after omicron infection are theoretically more marginal and in practice unknown, which limits the benefit-risk balance, and that is another aspect against rushing vaccination, no matter how safe these vaccines are, which are ”, Reasons the expert.
With a sixth wave that is on the way to infecting millions of people, the update of the strategy will affect hundreds of thousands: especially between 40 and 60 years, which are those who now have their turn for the booster doses: the oldest they are already mostly inoculated and for minors of that age there is still no scheduled memory puncture.
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