A large study in Israel, conducted by the Clalit Research Institute in collaboration with researchers from Harvard University, and published in The Lancet, investigated the efficacy of a third dose of the Pfizer/ BioNTech vaccine against Covid-19. Like many other vaccines, the one from Pfizer / BioNTech is given in two doses.
The study examined data on 728 321 individuals who received the third dose, compared with 728 321 corresponding controls who received only two doses at least five months previously. In those who gave the third dose, compared with those who took only two doses, the study found:
The Delta (B.1.617.2) variant was important in Israel during the study period, which occurred between July 30 and September 23, 2021, coinciding with Israel’s fourth wave of coronavirus infection and disease.
The study suggests that a third dose of vaccine is useful in overcoming severe Covid-19-related results related to people who took two doses of vaccine at least 5 months ago, the Clalit Research Institute said in a statement.
“The large scale of the study also allows a more accurate assessment of the vaccine’s efficacy over different periods, different subpopulations (by sex, age and number of comorbidities) and different serious outcomes (which are rarer and therefore require larger sample size).” A recent clinical trial conducted by BioNTech added a smaller sample size and did not consider the effect of the third dose for more serious outcomes, ”reads the statement.