Efficacy and Safety of NVX-CoV2373 in Adults in the United States and Mexico

Background:NVX-CoV2373 is an adjuvanted,recombinant spike protein nanoparticle vaccine that was shown to have clinical efficacy for the prevention of coronavirus disease 2019(Covid-19)in phase 2b-3 trials in the United Kingdom and South Africa,but its efficacy had not yet been tested in North America.Methods:We conducted a phase 3,randomized,observer-blinded,placebo-controlled trial in the United States and Mexico during the first half of 2021 to evaluate the efficacy and safety of NVX-CoV2373 in adults(≥18 years of age)who had not had severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)infection.Participants were randomly assigned in a 2:1 ratio to receive two doses of NVX-CoV2373 or placebo 21 days apart.The primary objective was to determine vaccine efficacy against reverse-transcriptase-polymerase-chain-reaction-confirmed Covid-19 occurring at least 7 days after the second dose.Vaccine efficacy against moderate-to-severe disease and against different variants was also assessed.