The effectiveness of the Pfizer-BioNTech vaccine drops after a few months in all age groups. This is an indication of a new Israeli study published in the New England Journal of Medicine. “Israel is an important observation point for the Pfizer vaccine efficacy study, because we started mass vaccination in December 2020 and the second dose of the vaccine was administered three weeks after the first dose, so we have I was able to observe the effectiveness of the double dose over time for longer than in other countries, “he explains Amit Huppert, researcher in biostatistics at Tel Aviv University’s medical school and co-author of the study.
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In the study, Huppert and colleagues compared the infection rate and severe disease rate of Covid between people who completed the vaccination course in January 2021 and those who completed it two months later, in March. “We found that, among the over 60s, in July the rate of infections in those who finished the vaccination cycle in January was 160% compared to those who, in that age group, had finished the cycle two months later” he explains. Huppert.
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“For people between the ages of 40 and 59, on the other hand, the rate of infections was 170% higher in those who had been vaccinated two months earlier. last vaccination gives a similar result: the infection rate is 160% compared to those who got vaccinated after “.
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These data confirm that the immunity conferred by the double dose of the vaccine, in all age groups, has dropped considerably within a few months of the last dose. “As the Delta variant spread to Israel in June – analysis of the viral genome showed that 98% of positives in June are attributable to the Delta variant – the increase in infection rates may have two contributing causes: the decrease in efficacy of the vaccine and the high infectivity of the Delta variant, which we know to have a higher viral load and mutations capable of evading the immune system “, points out Huppert. “To date we are not yet able to distinguish with absolute certainty the specific contribution of each of these two factors”.
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Huppert’s study goes in the same direction as another recent study which showed, for Pfizer vaccine, a decrease in efficacy from 96% in the period from one week to 2 months after the second dose to 84% in the period from 4-7 months after the second dose. “The indications that can be drawn from these studies, of course, vary according to the age group and the relative vulnerability – explains Huppert. – If I am over 70 and the immunizing capacity drops by 96% to 84%, then probably I should have the third dose. But if I’m in my 20s, and therefore have a much lower risk of severe disease, I can wait. ”
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To date, about 3 million people in Israel have received the third dose of Pfizer. “We researchers had to insist with the government to convince them of the opportunity of the third dose, given the rise in infections and hospitalizations in the summer – explains Huppert. – Because this summer, unlike what had been done in 2020, it was decided not to impose restrictions and lockdowns given that over 80% of the population was vaccinated and they did not want to run the risk of damaging the economy “.
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In addition to the spread of the Delta variant, what could be the cause of the decline in the effectiveness of the vaccination cycle? “It is normal for vaccines to lose their effectiveness over time. First of all because the amount of antibody tends to decrease – explains Huppert. – It is also thought that immune memory cells, or B and T lymphocytes, in responding to a new infection can be slower than the rate of replication of the virus. From what we have seen, Moderna’s vaccine appears to have a slightly slower decline in efficacy. One reason could be that it contains 100 micrograms of messenger RNA, while Pfizer’s vaccine does contains 30 “.
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