More than 85% of those vaccinated generate antibodies against COVID-19, according to a study of pharmacists

Vaccines against COVID-19 generate antibodies in more than 85 percent of those vaccinated, and this percentage rises to 97 percent when the infection has been previously passed, according to the results of the study ‘Security and Seroprevalence in the population vaccinated against the COVID-19 of the Sentinel Pharmacy Network of Castilla y León’, developed in 121 Castilian-Leon pharmacies with the participation of 4,000 citizens.

The objective of this study, presented this Friday at a press conference, has been to find out what happens in the general vaccinated population, put the antibody response and its duration into percentages. In addition, it has made it possible to record adverse events, identify the safest and most effective vaccination protocol, together with knowing how factors such as age, the vaccination protocol or having previously had the disease influence the immune response or its duration.

This study was carried out in a first phase between July 19 and 29, 2021, and in a second between November 26 and December 3. Two patient recruitment periods of just 10 days each, which have been enough to analyze more than 4,000 volunteer citizens, vaccinated and unvaccinated, and extract an X-ray of the situation.

Unlike other works, this study evaluates the efficacy of vaccination in the general population and in different age groups, while they are normally based on the efficacy of vaccination according to the number of hospital admissions or the severity of the symptoms of infected people when they enter or go to the health center.

The data from this study confirm that all the vaccines administered in Spain are “safe and effective” in the general population. However, it also advances that the immune response they generate “is not constant, it is not maintained over time and depends on different variables, such as the vaccination protocol or the age of the individuals.”

The tests carried out on the analyzed population reveal that the production of antibodies is high: the vaccines generate antibodies in more than 85 percent of those vaccinated. This percentage rises to 97 percent when the vaccinated have previously passed the infection.

This data contrasts with that of the unvaccinated population, in which only 4 percent have specific antibodies against the coronavirus. “It would correspond to asymptomatic patients who have had COVID-19”, detailed José Luis Nájera, secretary of CONCYL, member of the monitoring commission of the CyL Sentinel Pharmacy Network and one of the authors of the project.

The study indicates that there are certain vaccination protocols, especially those based on viral vector vaccines (AstraZeneca and Janssen), which generate a lower immune response. This has been verified in vaccination with Janssen, which offers a “significantly lower” response than with the rest of the vaccines and “even lower” if the person has not previously had the disease.

The same is true for people immunized with two doses of AstraZeneca. Hence, the study supports the need to give a new immunization to this sector of the population, reinforcing vaccination with sera based on messenger RNA (Pfizer and Moderna).

Likewise, the research determines that there are no significant differences in the generation of antibodies in the study between men and women, both genders responding in the same way.

It is also identified that exposure to the virus significantly influences the duration of the response. In people who have had the disease, the immunity provided by mRNA vaccines remains stable over time, even for more than 11 months. However, in vaccines based on viral vectors (AstraZeneca and Janssen), a reduction in response is already observed after 8 months.

On the contrary, in those people who have not previously had COVID-19, the vaccines decrease their efficacy in the production of antibodies after 6 months for the Pfizer and Moderna vaccines and after 3 months for those vaccinated with AstraZeneca and Janssen.

While in those vaccinated with Pfizer and Moderna, the immune response remains above 80 percent in all age ranges, the same does not occur in vaccines based on viral vectors (AstraZeneca and Janssen), where a “significant decline” the younger the population.

Regarding safety, the study indicates that the vaccination protocol, age or sex also influence the reported adverse events. In this sense, the Pfizer vaccine has emerged as the safest and the one with the fewest reports of adverse reactions.


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