The UC Davis School of Medicine is one of only 150 sites taking part in the major clinical trial that led to the federal government’s Emergency Use Authorization (EUA) of the Pfizer BioNTech COVID-19 vaccine in December, which helped pave the way for widespread vaccinations last winter and spring. During the trial’s latest phase, 60 participants here received a third dose of either vaccine or placebo to determine whether a booster is necessary, safe and effective against the original COVID-19 strain and the Delta variant. The ongoing worldwide trial involves 40,000 participants, including 225 over the last year at UC Davis. Principal investigators at the school of medicine include internal medicine chair Timothy E. Albertson, M.D., M.P.H., Ph.D., and Angela Haczku, M.D., Ph.D., associate dean for translational research.