Doctors are observing that the vaccines against covid-19 that use messenger RNA (for now that of Pfizer / BionTech and that of Moderna, which are the ones being used in Spain) cause more reaction in people who have previously passed the disease in the past. These cases correspond for example to health personnel who were already infected during the first or second wave since otherwise, it is not possible to ethically access a dose since in the prioritization prepared by the Ministry of Health it is placed in the last place to people who already have antibodies for having overcome the virus.

These observations are in the study phase. This week a preliminary investigation (not yet been peer-reviewed) came out by scientists from the Department of Microbiology at the Icahn School of Mount Sinai Hospital Hospital in New York ( USA ). In this short paper published on the MedRxiv repository, experts note that an important question that is emerging as covid-19 vaccines are implemented is whether people who already had a SARS-CoV-2 infection should receive one or two injections of the currently licensed mRNA vaccines.

This question arises because microbiologists have found that the antibody response to the first dose of the vaccine (messenger RNA) in individuals with pre-existing immunity (seropositive) is equal to or even greater than that found after the second dose in people who do not have previously been infected with SARS-CoV-2, as indicated in the study, carried out with 109 people (68 seronegative and 41 seropositive).

Antibodies detected after the first and second doses of the vaccines in previously seropositive and seronegative people for SARS-CoV-2, the virus that causes covid-19. PARIS TEAM. The number of antibodies of those vaccinated with pre-existing immunity is not only 10-20 times higher than those of those vaccinated without previous infection at the same times, but they also exceeded by more than 10 times the mean of antibodies measured in seronegative patients after the second dose of the vaccine detail the researchers, who emphasize that these first differences in immune responses will need further studies to see if they are maintained over time.


Furthermore, after comparing 231 people (148 seronegative and 83 seropositive), they have observed that in messenger RNA vaccines reactogenicity (common adverse reactions) is significantly higher in people who have been infected with SARS-CoV-2 in the past. Although they emphasize that in general the two vaccines were well tolerated and without any side effects that require additional medical attention.


Local side effects occur with comparable frequency, while systemic symptoms are significantly more common in people with pre-existing immunity,” the scientists have found. The study details that 159 of the 231 participants experienced some type of side effect after the first dose. Of these, 66% were seronegative and 73% previously seropositive. The most frequent reactions were symptoms localized at the injection site (pain, swelling, and erythema ), which occurred with equal frequency regardless of serological status at the time of vaccination and resolved spontaneously within days of vaccination.

In contrast, those vaccinated with pre-existing immunity experienced systemic side effects significantly higher than those vaccinated without prior antibodies, and these reactions were fatigue, headache, chills, fever, and muscle or joint pain. For this reason, the researchers, led by Florian Krammer, suggest that changing the vaccination policy to administer to these seropositive people only one dose of vaccine would not negatively affect their amount of antibodies would avoid unnecessary pain, and release many doses of vaccines, urgently needed.


In this sense, the vice president of the Spanish Association of Vaccinology (AEV), Dr. Fernando Moraga-Llop, said for a digital encounter with the readers of 20minutes that “in principle, all guidelines recommend vaccinating patients who have suffered the covid, as long as these patients are recovered (they are already without symptoms and have completed the isolation period), because it has been seen that the immunity produced by the vaccine is much higher than that produced by the disease

Although Moraga-Llop points out that we are observing, although it is a subject to study, that the vaccination of people who have suffered from the covid has more side effects than those vaccinated without having previously suffered from the covid. This subject, I repeat, must be studied he insists. In these cases, the pediatrician recommends HIV-positive people who have experienced adverse reactions after the administration of the first dose of the Pfizer or Moderna vaccines wait to administer.