Pfizer's booster shot 93% effective in preventing COVID, reduces mortality by 81%: Study

A third booster shot of the Pfizer Coronavirus vaccine decreases the rate of hospitalization from severe COVID-19 infection by 93%, and slashes the mortality by 81%, reducing the severity and the fatal symptoms from the respiratory ailment by 92%, an Israeli-American study published on Friday, October 29 in the Lancet journal has found. The study was conducted as many countries in the world have been witnessing the resurgence of COVID-19, driven predominantly by the delta (B.1.617.2) variant of SARS-CoV-2. 

Researchers from Clalit Health Services and Harvard University analyzed the data collected from nearly 730,000 individuals who received their third booster shot after being fully vaccinated against the COVID-19 in a two-dose regime. The participants were fully jabbed at least five months or more prior to their third dose. The first-ever study which has been peer-reviewed was conducted between July 30, 2021, to September 23, 2021, when the Delta strain of Coronavirus was at its peak worldwide.

Third booster shot administered due to 'potential waning immunity'

The volunteers, excluding healthcare workers, those that live in long-term care facilities, or are medically confined to their homes were given a third dose of mRNA COVID-19 vaccine as a booster dose due to the potential waning immunity over time and reduced effectiveness against the Delta variant. Researchers used data repositories of Israel's largest healthcare organization to evaluate the effectiveness of a third dose of the BNT162b2 mRNA vaccine, according to the study published on Friday.

“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,” researchers stated in the study. 

Despite several months of low pandemic cases in early 2021, Israel had experienced its fourth pandemic wave. This happened even when approximately 55% of the total population was vaccinated with two doses of the BNT162b2 mRNA COVID-19 vaccine. The population had received first and second doses over 21 days apart. “The increase in infections and hospitalizations of vaccinated individuals likely stems from a combination of waning vaccine immunity over time,” said the researchers, adding that most people in Israel were vaccinated 5–7 months ago.

And therefore, a third dose was given to at least half of the Israeli population aged at least 60 years within the first 2 weeks. It was found that the overall efficacy of the third vaccine dose compared with two doses was estimated to be 93% in preventing the COVID-19 infection, and the COVID-19-related admission to the hospital began to diverge around 6 days after vaccination. 

Image: Lancet Journal