Israeli data shows Pfizer booster 93% effective November 1, 2021 A third (booster) dose of the Pfizer-BioNTech vaccine against Covid-19 is 93 percent effective in protecting individuals against severe Covid-19-related outcomes, compared with two doses received at least five months earlier. This conclusion is based on data from Clalit Health Services, the largest of Israel’s four nationalized healthcare maintenance organizations. The study was published02249-2/fulltext) in The Lancet on October 29. “To our knowledge, the present study is the first to estimate the effectiveness of a third dose of an mRNA COVID-19 vaccine … against severe outcomes with adjustment for various...