The most comprehensive study to date regarding the efficacy of the third Pfizer-developed COVID booster vaccine, conducted by the Clalit Research Institute in collaboration with Harvard University, shows that a third dose reduces hospitalizations by 93%, reduces serious illness by 92%, and reduces corona-related deaths by 81%.
The researchers analyzed anonymous data of 728,321 patients of the Clalit HMO who received a third dose of the vaccine, compared to a control group that included 728,321 people who had received only two doses about five months or more before.
The data of the vaccines examined are in the period ranging from July 30 to Sept. 23, 2021, in parallel with the fourth corona wave in Israel, during which the Delta variant was the dominant strain in the country.
The matching between the study groups was performed based on an extensive set of demographic, geographic, and health characteristics related to risk for serious illness, health status, and health behaviors. Allocation to the study groups was performed dynamically based on the daily vaccination status and approximately 198,476 individuals switched from the unvaccinated group to the vaccinated group during the study period.
The findings suggested that the third vaccine dose reduced by 93% corona-related hospitalizations due to corona disease reduced by 92% serious illness, and reduced by 81% morbidity associated with corona morbidity.
The size of the study also allows for an accurate assessment of vaccine efficacy over different time periods, different subpopulations, and different serious outcomes.
Prof. Ran Blitzer, head of Clalit’s Innovation Division and director of the Clalit Institute for Research, said over the weekend that these results are “very important and give well-founded and valid information to anyone who is still hesitant about receiving the third dose – in Israel and other countries around the world.”
The outcome of the third Pfizer-developed booster vaccine administered to over 3,943,000 Israelis in recent weeks is apparently taking effect, as the fourth COVID-19 wave in country is fading away and as the country recorded the lowest COVID-19 stats in months.