Abigail Klein Leichman
November 14

The protection achieved by a third or fourth dose of the Pfizer–BioNTech Covid-19 vaccine is significantly stronger than that of two doses alone, but weakens over the course of about four months, say researchers at Israel’s Sheba Medical Center and New York’s Columbia University.

The study, published in the New England Journal of Medicine, measured both immune response and effectiveness of the vaccine in preventing infection with the Omicron variant of the SARS-CoV-2 virus.

The overall vaccine effectiveness in preventing Omicron infection was 40% during the first six months after the booster, and as high as 50% during the initial months. The boosters’ effectiveness peaked within a month of the injection.

“Our latest research sheds further light on the direct relationship between antibodies and protection against coronavirus infection, including Omicron,” said Prof. Gili Regev-Yochay, director of the Infectious Diseases Unit at Sheba Medical Center.

“With protection clearly waning after four months, individuals and health systems must plan their booster timing wisely, taking into consideration not only surges in infection but also personal medical conditions, upcoming events and travel, and higher-risk seasons.”

The study, conducted on a cohort of about 6,000 healthcare workers at Sheba, was led by Regev-Yochay with Dr. Michal Canetti at Columbia University.