Pfizer scans millions of health records to see how well its COVID vaccines worked

This study aimed to understand how well different versions of the Pfizer-BioNTech COVID-19 vaccine worked in the real world. Researchers analyzed existing health records from nearly 20 million people in California and Louisiana to see how well the vaccines prevented death, severe illness requiring hospitalization, and other healthcare visits. No new participants were enrolled; the study used data already collected from state vaccine registries and insurance claims.