After receiving the complete schedule of a vaccine -either against covid-19 or against another type of infectious disease, such as Hepatitis B- there are cases in which the immune system either does not produce a sufficient response or, failing that, it does not produce it directly.

This not only occurs in people in whom, a priori, a minor immune response, such as patients with immunodeficiencies or with other specific pathologies, but it can also occur in the general population although, according to experts, the probability is very low.

This week, a man with the two doses of the vaccine died of Covid at the Bellvitge Hospital, on which the doctors at the center reported that he had developed a low level of antibodies. Mass vaccination implies that there are people with particularities that are not taken into account when it comes to their vaccination, and that affect your immune response. But does that imply that they are unprotected? Do they need an extra dose?

Immunity, a question beyond antibodies

One of the elements to consider when addressing the issue of immunity is that “measuring only the level of antibodies leaves the picture of the immune response half complete“, he remembers, in an interview with 20minutos, the specialist in Clinical Immunology at the Hospital Universitario de Canarias and member of the Spanish Society of Immunology, Yvelise Barrios.

“Measuring just the level of antibodies leaves the picture of the immune response half complete”

There are two types of responses in our immune system: the humoral, which is the one that can be measured through antibodies, and the cellular. The latter is “more diverse”, in the words of the doctor, and is “capable of responding even when there are small changes (such as variants) that do affect the humoral response.” That is why not generating a sufficient immune response can depend on multiple factors, according to experts.

To what extent does it affect the general population?

There are groups of population for which a worse immune response is assumed. These are, for example, “patients who have immunodeficiencies, cancer patients, those who have a disease that prevents them from having a healthy immune system or those who take treatments to suppress their immune response, such as transplants,” explains Dr. Barrios. But “pregnant women also have a physiological immunosuppression,” adds Dr. Julio García Rodríguez, head of the Microbiology Service at Hospital La Paz.

Cantabria adds 300 cases and increases hospitalized and admitted to ICU

However, according to both, It is possible that among the general population there are also people who are less able to respond to the full course of a vaccine, as well as “Each person responds differently to the disease,” says García in an interview with 20minutos. “Just as the virus infects two patients, one can be taken to the ICU and another can practically not even find out,” the doctor clarifies, with which “that difference that we see in the natural infection in the general population, we can also see it in vaccination, “he clarifies.

In addition, in full campaign to fight against Covid “many people are massively vaccinated, some of whom may have some unknown immune system problem“, explains Barrios, a specialist in immunology, either because” they have not been diagnosed “, or because” this problem has gone unnoticed “, which could explain these” anecdotal cases “. In this line, the immunologist emphasizes that” it is a very, very small percentage of the general population “that it affects.

Is the vaccine or the immune system responsible?

These cases “have to do with the immune system and with situations intrinsic to each individual,” explains Barrios, “which on some occasions we know in advance, because we already have a diagnosis,” he insists. But it can also depend on external factors. According to the specialist, there could be “a multitude of causes” which could even include a “failure in the cold chain” of the vials.

“It not only happens with vaccines against covid, but also with measles, hepatitis or chickenpox, among others”

This not only occurs with the covid, but also occurs “with all vaccines: hepatitis, measles or chicken pox,” stresses, for his part, García. The doctor from La Paz emphasizes that, “in fact, not all vaccines have the same efficacy “, so it may also depend on the type of serum used.

Are these people unprotected ?: a matter of percentages

However, the question arises as to whether or not these -few- individuals are unprotected against covid and other diseases. The answer to this question, according to both experts, is not a binary question that can be answered with ‘yes’ or ‘no’, but rather it is necessary to speak “in percentages”. Namely, that these people could develop a milder infection, although the immune response was also.

A man receives a dose of a vaccine against covid-19 in the borough of the Bronx, New York (USA).

In cases where this weak response is already assumed, such as “kidney transplants, we know that, after two doses, 65% of patients have had a measured humoral response (antibodies), “Barrios explains about his own experience.

To this, García points out, we must add that the fact that “someone may not have neutralizing antibodies does not mean that they are unprotected”, stands out, because “it can have a good cellular immunity response,” he adds.

Both agree, however, that since, for the moment, the way for the general population to know what the immune response has been generated is “rperforming very specific tests“, explains the head of microbiology of La Paz, the best way to avoid a serious infection is” to continue with precautions while we do not have herd immunity “, a milestone for which, according to Dr. Barrios,” we are still far below “.

The solution: a third dose to intensify the regimen?

The third dose debate is already on the table. But experts warn that it is important to carry out “studies of antibodies and cellular immunity to have the evidence in hand on how to make the best indication”, highlights Dr. Barrios.

In this way, the short-term goal in research on the effects of vaccination could focus on answer how “optimize the guidelines and knowing how to get a better performance in more targeted groups “and answer” if a third dose is going to be necessary or if some vaccines are better than others “.

The inoculation of the second dose to the elderly at the 'Javalambre' Residence in Teruel takes place this Tuesday.

For his part, Dr. García stresses that “We still don’t know if these people are unprotected or not” and that if a third dose is to be inoculated, it is “because we are beginning to have sufficient evidence” in still unexplored terrain.

However, previous experience tells us that “there are many vaccines where different guidelines have had to be implemented”, so that “intensifying the pattern managed to reverse” the disease, highlights the doctor from the Hospital Universitario de Canarias.

The risk of contagion with the complete pattern

Regarding the number of people with the complete pattern who are being infected, the experts explain that, although there are some cases, it is not a generalized situation. “Of the number of people admitted to hospitals right now, the vast majority are not vaccinated, and of those who are vaccinated, they are half vaccinated“, highlights Barrios.

“If we start to see hundreds of vaccinated people who are getting infected, we have a problem, but right now it is not the situation, “says García.

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