The Clalit Research Institute, in collaboration with researchers from Harvard University, analyzed one of the world’s largest integrated health record databases to examine the effectiveness of the third dose of the Pfizer/BioNTech BNT162B2 vaccine against the Delta variant of SARS-CoV-2. The study provides the largest peer-reviewed evaluation of the effectiveness of a third “booster” dose of a COVID-19 vaccine in a nationwide mass-vaccination setting. The study was conducted in Israel. It is published in The Lancet journal.