Photo Credit: Yonatan Sindel/Flash90
A woman receives the booster vaccine shot at a Clalit healthcare center in Jerusalem, October 3, 2021.

The Ivan and Francesca Berkowitz Family Living Laboratory Collaboration at Harvard Medical School and Clalit Research Institute on Friday published in The Lancet weekly peer-reviewed general medical journal the results of their extensive study on the effectiveness of the third “booster” vaccine in Israel (Effectiveness of a third dose of the BNT162b2 mRNA COVID-19 vaccine for preventing severe outcomes in Israel: an observational study).

The study authors noted that many countries are experiencing a resurgence of COVID-19, driven predominantly by the delta variant. These countries are considering a third dose of the Pfizer COVID-19 vaccine as a booster dose to address the diminishing immunity over time and, resulting in reduced effectiveness against the delta variant.


“We aimed to use the data repositories of Israel’s largest healthcare organization to evaluate the effectiveness of a third dose of the BNT162b2 mRNA vaccine for preventing severe COVID-19 outcomes,” the study authors stated.

Using data from Clalit Health Services, which provides mandatory healthcare coverage for more than half of Israel’s population, the study matched, 1:1, individuals receiving a third vaccine dose between July 30, 2020, and Sept 23, 2021, with demographically and clinically similar controls who did not receive the third dose.

Eligible participants had received the second vaccine dose at least 5 months before the recruitment date, had no previous documented infection, and had no contact with the healthcare system in the 3 days before recruitment. The study excluded healthcare workers, residents of long-term care facilities, and individuals who are medically confined to their homes.

1,158,269 individuals were eligible to be included in the third dose group. Following matching, the third dose and control groups each included 728,321 individuals. Participants had a median age of 52, and 51% were female. The median follow-up time was 13 days in both groups. Vaccine effectiveness was evaluated at least 7 days after receipt of the third dose—compared with receiving only two doses at least 5 months ago—was estimated to be 93% for admission to hospital, 92% for severe disease, and 81% for COVID-19-related death.

The study authors concluded: Our findings suggest that a third dose of the BNT162b2 mRNA vaccine is effective in protecting individuals against severe COVID-19-related outcomes, compared with receiving only two doses at least 5 months ago.


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