Pfizer Vaccine Sharply Reduces Symptomatic Covid Cases: Report Pfizer Vaccine Sharply Reduces Symptomatic Covid Cases: Report The Clalit Research Institute analysed data on 1.2 million people, about half of whom had received the Pfizer-BioNTech vaccine. Researchers compared patients who received the vaccine with similar individuals who hadn't. Tel Aviv: Pfizer-BioNTech's COVID-19 vaccine appears to reduce symptomatic coronavirus infections by more than 90 per cent in the real world, according to Israeli researchers. According to CNN, the preliminary findings published on Monday suggest that the vaccine remains remarkably effective in a mass vaccination campaign -- outside the carefully controlled conditions of a clinical trial.