Largest Real-World Study Of 1.2 Million People Shows Pfizer COVID-19 Vaccine Is 94 Percent Effective

This is great news. Image credit: Prostock-studio/

The largest real-world study on the vaccine efficacy of the Pfizer/BioNTech vaccine (AKA BNT162b2) has found the jab is 94 percent effective at preventing symptomatic infection of COVID-19. The study looked at almost 1.2 million people vaccinated in Israel.

“This study estimates a high effectiveness of the BNT162b2 vaccine for preventing symptomatic COVID-19 in a noncontrolled setting, similar to the vaccine efficacy reported in the randomized trial,” the authors wrote on the paper published in the New England Journal of Medicine.

“Our study also suggests that effectiveness is high for the more serious outcomes: hospitalization, severe illness, and death. Furthermore, the estimated benefit increases in magnitude as time passes. These results strengthen the expectation that newly approved vaccines can help to mitigate the profound global effects of the COVID-19 pandemic.”

The study involved 1,193,236 people divided into two well-matched groups: vaccinated individuals and unvaccinated individuals. This experimental design is known as a case-control study and it is very useful to understand the actual effectiveness of a vaccine or a drug in a real-world setting. It makes sure that people from the vaccinated group are matched against very similar individuals in the control group.

“Each person who was vaccinated from 20 December 2020 to 01 Feb 2021 was 'matched' to control of similar age, sex, geographical, clinical and other characteristics. Crucially, the 'control' person was NOT vaccinated, while the 'case' person was,” Dr Peter English, the previous Chair of the BMA Public Health Medicine Committee, who was not involved in this study, explained. “This allowed the investigators to compare a number of outcomes between cases and controls; and it allows them to infer that differences may be a consequence of vaccination."

The trial took place during the highest incidence of cases in Israel, which peaked in late January 2021 with almost 12,000 new cases in a day. The prevalent variant of the disease was the UK variant, which the vaccine appears to be effective against. Cases of the South African variant were too rare for such an estimate to be made in that case.

However, the study didn't look at the possibility of vaccination stopping asymptomatic cases. Other studies also from Israel suggest that this is happening, which if confirmed would be very promising news. The vaccination program alone would be enough to curb the spread of the disease and we could soon say goodbye to behavioral measures such as lockdowns and social distancing to keep the virus at bay.

For more information about COVID-19, check out the IFLScience COVID-19 hub where you can follow the current state of the pandemic, the progress of vaccine development, and further insights into the disease. 


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