The Pfizer-BioNTech vaccine against Covid-19 becomes less effective six months after the administration of the second dose. The results of the research were published in the New England Journal of Medicine, according to new Israeli research published in the New England Journal of Medicine.
Nearly 5,000 health care workers, who had been vaccinated, were studied and the results were similar to earlier findings that were published by Pfizer and Kaiser Permanente in the Lancet, a few days ago, strengthening the requirement of a third dose or booster shot.
The Israeli study had over 4,800 healthcare workers who had taken both doses of the Pfizer-BioNTech vaccine. The antibody response of these workers was tested monthly starting from December 19, 2020, and continuing up to July 9, 2021.
The immune response kept decreasing each month. The researchers also noted that three groups: men, people over the age of 65, and the immunosuppressed had the largest decline in efficacy.
They said that the antibody level fell briskly in the early period of approximately 70 to 80 days and then tapered off and fell slowly.
The researchers also reported that there was a “striking difference” in the antibody response of those who had been vaccinated and those who had recovered from COVID-19. They concluded that the overall immune response among those who were naturally affected was higher than among those who had been fully vaccinated.
This might explain why there was a much lower incidence of breakthrough cases of infection among those who had been infected by COVID-19 when compared with those who had taken two doses of the vaccine.
Dr. Gili Regev Yochay, who was the lead author of the study and is the chief of infectious disease epidemiology at Sheba Medical Center noted that the new study, together with the earlier studies, contributed to the decision of the Israeli government to vaccinate its population with a third dose or booster shot.
The studies have shown that the Pfizer vaccine is effective in preventing hospitalizations of infected people by 90 percent for at least six months. They have also shown that its efficacy can fall from 88 to 47
percent after six months.
(With inputs from agencies)
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