The complexity of science in general, and medicine in particular, makes the majority of the population appeal to researchers as if they were prophets. Not understanding how they reached their conclusions, we interpret them as revelations. For that same reason, we hope that they will answer any question we may have and, above all, that they do so with a certainty that is rarely seen in true science.
However, there are questions to which the answer, whether you are a scientist or not, can be answered with common sense. The clearest example of this is the main question that exists about Covid-19 vaccines: How long does the immunity they provide last? How antibody levels evolve over time and other indications suggest that they can maintain adequate protection for a longer or shorter period, but the reality is that We will only know how long the immunity of the new sera lasts when vaccinated people begin to be infected with Covid-19 and develop symptoms.
The answer, however, has its nuances. First, because the vaccines themselves do not prevent SARS-CoV-2 infection but rather the development of symptomatic disease. There have already been cases of people with a complete vaccination schedule who have been infected again, although there have been very few and with mild symptoms. Second, because immunity does not last the same in all people. Sex, age, diseases suffered and other characteristics of each one influence the duration of protection.
The studies carried out so far are based on monitoring people who have already been vaccinated and checking their status from time to time to see if they have been infected with Covid or there are indications that they have lost part of their protection, such as a notable drop in the level. of antibodies achieved two weeks after the last injection, usually the reference that marks the maximum point of protection.
So far, several studies have been carried out to check how the immunization of the different vaccines evolves. Obviously, those approved before will have proven, as of today, a longer duration of immunity.
Duration of Pfizer Immunity
Comirnaty, the vaccine developed by the German laboratory BioNTech and the North American Pfizer, was the first to be authorized in a Western country, on December 11, 2020 in the United States and 10 days later in the European Union.
The Centers for Disease Control and Prevention in the United States, known as CDC, have published a study carried out among healthcare personnel, who were among the first groups to be vaccinated, to verify the efficacy of the vaccine beyond clinical trials, and He noted that immunity lasted beyond three months (The first cutoff of the study results was at the end of March).
Two factors must be taken into account: as they are health professionals, the average age was notably lower than that of other population groups that were vaccinated in the first days of the campaign; and, on the other hand, the study also included people who had received a single dose so far and who, in a small part, had also been vaccinated with the Moderna preparation.
BioNTech co-founder, Ugur Sahin, indicated in a press conference that antibody levels begin to decline six months after the second dose was inoculated, ensuring that a third would be needed between 9 and 12 months later to preserve the dose. maximum immunity against coronavirus. Although this statement has not been corroborated by independent researchers, it is a feasible possibility since the developer laboratory has first-hand the most up-to-date data on those people who were the first to be vaccinated, that is, those who received the prick as part of a clinical trial months before the vaccine was approved.
Duration of Moderna’s immunity
The second vaccine to be approved in both the United States and Europe was developed by the North American laboratory Moderna and, like Comirnaty, is based on messenger RNA technology.
An article recently published in the medical journal New England Journal of Medicine examined 33 people from the first clinical trial carried out with this vaccine, that is, the first to receive it in the world. 180 days after the second dose has been inoculated, that is, six months after completing the vaccination regimen, antibody activity remained high. This circumstance occurred in all age groups, although in people aged 56 years and older the presence of antibodies was reduced somewhat more than in those under that age.
Despite these data, the vice president of Moderna for Europe, Dan Staner, explained in an interview with Invertia that a third dose of the preparation would possibly have to be administered between six and twelve months after said second dose since, at nine months , the activity of the neutralizing antibodies has decreased and, if we refer to the Beta variant (formerly known as South African), that activity is reduced six or seven times more.
Duration of AstraZeneca immunity
The approval of Vaxzevria, the immunization against Covid-19 developed by AstraZeneca and the University of Oxford, by the European Medicines Agency (EMA) arrived on January 29. At the end of April, the Agency itself issued a report on the safety and efficacy of the vaccine, due to the alarm generated by the cases of thrombosis associated with the inoculation of serum.
This report made an estimate of the lives saved by the vaccine against deaths due to thrombi caused as a secondary effect of the vaccine in three scenarios with different infection rates and it was concluded that the benefit was unquestionable. To make this estimate, the EMA considered an efficiency of 80% during a period of four months. These four months have been taken by some as a minimum duration, although there are no subsequent studies that have confirmed or denied this estimate.
One particularity of Vaxzevria must be taken into account, and that is that the second dose is inoculated between 4 and 12 weeks after the first injection. A post-approval study indicated that the greatest efficacy was achieved by postponing the booster dose until week 12, something that has subsequently been standardized to also take advantage of all the vaccines that arrived first to immunize more people and not reserve part for the second dose.
So that, the AstraZeneca immunity duration counter would start three months after receiving the first dose (In Spain, the delay is greater since Health decided to postpone the reinforcement for another month to wait for the results of the CombiVacs study). The first doses began to be given in February, so real-life studies will still take time to have results on how long the immunity generated by Vaxzevria lasts.
Duration of Janssen’s immunity
It is the last of the vaccines approved in the European Union and the United States so far. The authorization from the EMA arrived on March 11 and has the advantage of being a single dose, so it has been possible to start counting the immunity generated without having to wait at least three weeks for a second puncture of the remaining ones.
However, there were two factors that have delayed the immunity timer. The first was that the United States decided to suspend the use of this vaccine for a few days until the risk of thrombi was determined (minimal, as in the case of AstraZeneca). The second is that Janssen’s first major shipment of vaccines arrived in Europe in the second half of AprilTherefore, the first vaccinated have barely a month and a half of immunity.
In May they appeared published in the New England Journal of Medicine the results of the first clinical trial conducted by Johnson & Johnson (Janssen’s parent), which involved 805 people. The study made a follow-up of the vaccinated until day 71 after vaccination, that is, about two and a half months later, and confirmed that the levels of antibodies remained stable until that moment in both young adults and those over 65 years of age.
It will be after the summer when it begins to become clear how powerful the protection is generated by messenger RNA vaccines, the first to be approved, in order to offer a third dose, as the directors of Pfizer and Moderna have warned, between the end of this year and the beginning of the next.
In the case of adenovirus vector-based vaccines, those developed by AstraZeneca and Janssen, we will have to wait a little longer, but it is possible that in the last trimester there will already be reliable data that give clues about the duration of immunity and the need for reinforce vaccination annually.