The risk of ongoing vaccination

The phrase is from the head of Strategy for Biological Health Threats and Vaccines of the European Medicines Agency (EMA), Marco Cavalieri, who yesterday expressed doubts about the need to administer booster doses of the vaccine against COVID-19 "continually". The warning from the highest European authority on vaccination coincides with what was previously pointed out by several immunologists, such as the professor of Immunology at the Center for Biomedical Research (CINBIO) of the University of Vigo, Africa González.

Cavalieri said that the EMA will need to see scientific data on fourth doses before it can make any recommendations. "We are quite concerned about a strategy that involves repeated vaccination in the short term."he admitted. He showed his understanding for the fact that third doses are administered "due to the current epidemiological situation", but warned that vaccination cannot be repeated "continuously". Thus, he proposed "to start thinking about booster doses more spaced in time that are synchronized with winter, as is done with the flu."

"Repeated administration can produce inverse effects to those expected, with a lower response"

Africa González - Professor of Immunology at UVigo


Immunologist Africa González has been warning for some time about the risk of repeating doses very repeatedly. In a report published on December 19 in FARO, a medium that belongs to the same editorial group as this newspaper, on "vaccine fatigue", the scientist and popularizer pointed out that this can induce an effect called "tolerance": "This is what is intended with allergy vaccines and is motivated by the activation of regulatory cells. Therefore, not always excess and repetition is necessary, nor does it obtain the desired effect ".

Africa González- Professor of Immunology at UVigo Alba Villar

Asked again about this question, the author of the informative book "Immuno Power: Know and strengthen your defenses" He stressed yesterday that "repeated administration can produce inverse effects to those expected, with less response. This is mediated by an exhausted lymphocyte, and also by an increase in regulatory T cells, and the type of memory that is generated is affected, especially that of B lymphocytes ”.

The expert refers to scientific evidence such as that pointed out by a US study published in July 2019 in the journal "Nature Communications". It notes that repeat vaccination may contribute to less effective seasonal flu vaccines. It should be noted that this research refers to annual vaccination against influenza, which includes several strains of types A and B. The study, led by Surender Khurana, of the US drug agency (FDA), concluded that repeated vaccination reduces antibody affinity maturation in different influenza vaccine platforms.

On the other hand, Africa González adds that Repeated vaccination against COVID-19 could lead to an overproduction of antibodies that could lead to problems. There is some scientific debate about the fact of administering booster doses with the original vaccine, not adapted to omicron. Some experts believe that injecting various boosters of the vaccine designed for the Wuhan virus could reduce the effectiveness of future vaccines. Others, like the celebrated American immunologist Anthony Fauci, deny that the so-called "original antigenic sin" can occur, according to which the immune system relies on the memory of its first encounter with a virus, which sometimes leads to a weaker immune response when later faced with another version of the pathogen.

"For now there are no data that point to this, nor previous experiences, but at an experimental level there are data that repeated doses and little spaced in time induce a lower immune response"

Africa González


The UVigo scientist has pointed out that there would be no problem in shortening the time between the second and third dose from 6 to 5 months, given the increase in transmission. "It would help to increase the production of antibodies and therefore to reduce the severity of the infection, as well as to reinforce the memory immunity, already acquired with the first two doses," he stressed. This is especially necessary for the vulnerable, elderly, who take immunosuppressive drugs or are immunodeficient, since the third administration confers immunity similar to the rest of the population with two doses. It is not clear that a third dose is indiscriminately necessary for the general population, especially in young people who do not suffer from serious disease ”, concludes the immunologist.

Precisely the clinical subcommittee that advises the Xunta yesterday showed its concern about the uncertainty about reducing by half –from 6 to 3 months– the period of time between the administration of the second dose and the booster dose.


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