Pfizer COVID-19 vaccine works well outside of clinical trials, study finds

Pharmacist prepares vaccine.

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Pfizer and BioNTech’s COVID-19 vaccine is proving as effective in real-world settings as it did in clinical testing, according to a study in the New England Journal of Medicine (NEJM) co-authored by Harvard T.H. Chan School of Public Health researchers.

The study looked at data on more than 500,000 people who received the vaccine in Israel between Dec. 20, 2020, and Feb. 1, 2021 and compared it with a similarly sized group of people who were not vaccinated. The vaccine was 94 percent effective against symptomatic illness a week after the second dose, according to the findings. It was also 92 percent effective against severe disease. The data were collected through Clalit Health Services, a research arm of Israel’s largest health care provider.

“In all studies of vaccine effectiveness, a major challenge is to ensure that those we are comparing to identify the vaccine’s effect are similar in the other characteristics that may predict whether they get infected or ill,” said Marc Lipsitch, professor of epidemiology, director of the Center for Communicable Disease Dynamics, and a co-author of the NEJM paper, in a Feb. 24, 2021, New York Times article. “Clalit’s extraordinary database made it possible to design a study that addressed these challenges.”

In a Feb. 25, 2021, Time article, Lipsitch said the study findings are “close to the best possible news.” Yet, he said, many important questions remain, including how long immunity from the vaccine lasts.