Background Vaccines are needed to prevent coronavirus disease 2019 (Covid-19) and to
protect persons who are at high risk for complications. The mRNA-1273 vaccine is a lipid
nanoparticle–encapsulated mRNA-based vaccine that encodes the prefusion stabilized full-
length spike protein of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2),
the virus that causes Covid-19. Methods This phase 3 randomized, observer-blinded,
placebo-controlled trial was conducted at 99 centers across the United States. Persons at …

Individuals deemed to be at high risk for SARS-COV-2 infection or its complications were
randomised to receive two intramuscular injections of the mRNA-1273 vaccine 100µg
against SARS-COV-2 (n= 15,210) or placebo (n= 15,210) 28 days apart in this phase 3 trial,
with > 96% of participants receiving both their injections, and 2.2% having serological
and/or virological evidence of SARS-COV-2 infection at baseline. Compared with placebo,
symptomatic COVID-19 illness occurred in significantly fewer mRNA-1273 vaccine …