Polack FP, Thomas SJ, Kitchin N, et al. - As tens of millions of people have been afflicted by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and the resulting coronavirus disease 2019 (Covid-19) in a worldwide pandemic, there is an urgent necessity for safe and effective vaccines. In an ongoing multinational, placebo-controlled, observer-blinded, pivotal efficacy trial, a total of 43,448 participants were administered two doses, 21 days apart, of either placebo or the BNT162b2 vaccine candidate (30 μg per dose). BNT162b2 is a lipid nanoparticle–formulated, nucleoside-modified RNA vaccine that encodes a prefusion stabilized, membrane-anchored SARS-CoV-2 full-length spike protein. Outcomes suggest that in persons 16 years of age or older, the two-dose regimen of BNT162b2 afforded 95% protection against Covid-19. Its safety profile was similar to that of other viral vaccines over a median of 2 months.