A third dose of the Pfizer coronavirus vaccine reduces the risk of COVID-related death by 90 percent, according to an Israeli study conducted on people aged 50 and older and published Thursday in the New England Journal of Medicine.
Over 4 million Israelis have already received their third, booster shot so far.
The study, conducted by Clalit Health Services, followed up on all the HMO’s clients ages 50 and up who received the second dose of the vaccine at least five months earlier – and compared the fatality rates from COVID-19 among the group that received the booster shot to the group that did not.
The study was conducted during the delta variant wave, between August 6, 2021 – a week after the booster shot was approved for adults in Israel – and September 29, 2021. The researchers surveyed the data on 843,208 Clalit members age 50 and up who received the second dose of the vaccine.
Similar to previous studies from Clalit, Israel’s largest HMO, on the effectiveness of the vaccines, the methods for the present study also included monitoring two groups, in which those who receive the booster are then moved from the two-dose group to the three-dose group.
The large size of the pool of participants allowed a precise estimate of the correlation between receiving the booster shot and the fatality rates resulting from coronavirus infection. The average age of the group in the study was 68.5, and at the end of the period of the study, 90 percent of this group had received the third dose of the vaccine.
The study found that among those who received the booster – starting from a week after the shot – the fatality rate from Covid fell by 90 percent. Among men, it fell by 88 percent and for women 94 percent, compared to the group that received only the first two doses.
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“The results of the research that we conducted unambiguously show that the booster vaccine is clearly correlated with a reduction in the risk of death from Covid, including the delta variant. There are very few interventions in the medical world that can be attributed with a tenfold reduction in the risk of death, as we found for the booster vaccine,” said Dr. Doron Netzer, Clalit’s head of community medical services.
Nonetheless, the results are not a surprise; they match what laboratory studies – and the infection rates beginning in July when the fourth wave of Covid began – the delta wave, during which it was found that the immunological protection of the first two doses faded significantly after five or six months.
In October, another study was published in the New England Journal, conducted at the Sheba Medical Center in Tel Hashomer and led by Prof. Gili Regev-Yochay, director of the infectious disease epidemiology unit at Sheba. The study found that during the six-month period after the second dose of the vaccine was received, a clear and continued drop in the levels of IgG antibodies was seen.
These are the antibodies that appear about two weeks after the vaccination, and are partly responsible for forming the immunological memory – both on the level of the neutralizing antibodies, the group of antibodies capable of preventing the binding and penetration of the virus into the cells and in doing so neutralizing the virus – which seem to have a central role in preventing the disease.
It was also found that at first the levels of neutralizing antibodies fell sharply, and from the third month after the second dose of the vaccine the levels fell at a more moderate pace. The chances a healthy woman between the ages of 18 and 45 would completely lack the neutralizing antibody capability was 2.5 percent; 5 percent for women ages 45 through 65; and 6 percent for those 65 and older.