“We are not going to get better protection by giving one and another dose”


R. Ibarra




What is the level of immunity necessary to protect us against the coronavirus? How many doses will be needed? “Each dose of vaccine constitutes a stimulus that forces the immune system to produce more antibodies and more specific lymphocytes against the virus,” explains Rafael Correa Rocha, from the Gregorio Marañón Hospital Immuno-regulation Laboratory in Madrid.

But the question is, he points out, “to what extent is it necessary to increase that immunity or if excessive stimulation could be counterproductive by causing an exhaustion of the immune system’s capacity to generate these responses or compromising immunity against other pathogens.”

As indicated by the Spanish Society of Immunology (SEI), it states, “by giving one and another dose to infinity, without time intervals, we are not going to achieve better protection.”

This researcher assures that “individuals who become infected with the Ómicron variant will generate additional immunity similar to that of receiving a dose of vaccine, so that level of protection acquired when infected probably makes a booster dose unnecessary in a period for several months.”

In addition, this immunologist points out, the effectiveness of a vaccine in generating immunity depends on many factors: «individuals, such as their genetic characteristics, the ability of their immune system to respond to the stimulus of the vaccine, which can in turn be influenced by factors such as being overweight, smoking, etc.».

Individuals who become infected with the Omicron variant will generate additional immunity similar to that of receiving a dose of vaccine

Another very relevant factor is age. In children, he indicates, “their immune system has great plasticity and response capacity, as it is a system in the process of maturation and learning, while in the elderly this response capacity is more diminished. For all these reasons, the same dose of vaccine will induce very different immunity and protection depending on the individual.”

Thus, he comments, “it is very likely that the magnitude of the immunity and immunological memory generated in children confers a high level of protection on them, which perhaps (studies are required to clarify this) make booster doses unnecessary.”

An example of this is that the immunity generated in childhood against diseases such as measles or chicken pox lasts over time and it is rarely necessary to increase immunological memory with booster doses, he points out, “while, in an elderly individual, or population at risk where the immune response capacity is diminished, booster doses are probably more necessary, in order to maintain an adequate protection threshold».

The same dose of vaccine will induce very different immunity and protection depending on the individual

But in addition to the factors inherent to the heterogeneity between individuals, “the immunity generated will be more or less effective depending on the characteristics of the virus and its rate of mutation and transmission.”

Thus, he explains, the specific immunity generated thanks to a vaccination or spontaneous exposure to the virus will be ineffective if the virus has mutated and the targets to which that immune response was directed have changed.

As with the flu, “if the virus changes and a new strain is different from the previous one, the immunity generated against the previous virus will not be able to recognize and control the new virus, since the molecules it recognized as targets are no longer they are or are not the same in the new virus.

Correa has coordinated with Marjorie Pion a study to evaluate how many days it takes for this protective immunological memory to be generated after completing the two-dose vaccination schedule (Pfizer/Biontech and Moderna). The researchers studied the immune response to the vaccine in volunteers from the hospital, measuring the cellular response three, seven and fourteen days after vaccination.

The results, published in « Frontiers Immunology », show that the maximum level of protection with the Pfizer-Biontech vaccine is not reached until seven days after receiving the second dose and, in the case of the Moderna vaccine, the level of cellular response generated is higher than that produced by Pfizer, but the maximum level of protection is not reached until 14 days later.

“What has been seen, and this justifies the fact that the third dose is being administered, is that the immunological memory decreases over time after receiving the second doses. And this third dose has been shown to boost that immune reserve or immunity again.”

But another great unknown is what is the level that must be maintained to be protected? We do not know, says Correa, “if that level is 1,000 or 100. Therefore, the third dose will produce benefits or increase immunity, but we do not know if successive doses will be necessary or reaching a level, even if it is low, of immunity , we can be protected in the long term, as occurs with other vaccines in which a single dose is sufficient, since for many years not having to give a booster dose ».

What is the level that must be maintained to be protected? We don’t know if that level is 1,000 or 100

Fortunately, he concludes, “we are seeing that the vaccines are effective and deaths or clinical complications have been drastically reduced among the vaccinated population, thanks to the fact that the immunity induced by the vaccine is capable of controlling the infection much more effectively. The answer to whether more booster doses will be needed will be given by ongoing studies that determine what level of immunological memory must be maintained to ensure protection. With these data it will be possible to determine with greater specificity which sectors of the population or which individuals need booster doses and in which they are not necessary».

For Correa, «A more effective strategy to better control the epidemic at a global level would be to first guarantee vaccination with complete guidelines in the greatest number of countries and in the entire territory, rather than propose successive periodic doses without even having sufficient information to establish whether they are essential to guarantee the protection they confer.

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