A Study to Evaluate the Efficacy, Immune Response, and Safety of a COVID-19 Vaccine in Adults ≥ 18 Years With a Pediatric Expansion in Adolescents (12 to<18 Years) at Risk for SARS-CoV-2

This is a phase 3, randomized, observer-blinded, placebo-controlled study to evaluate the efficacy, safety, and immunogenicity of SARS-CoV-2 rS with Matrix-M1 adjuvant in adult participants and adolescent participants. Additionally providing a Booster Dose to fully vaccinated participants. A substudy is to be conducted at selected sites to evaluate the safety and immunogenicity of a fourth dose (second booster) of NVX-CoV2373 in adults and adolescents, previously fully vaccinated and subsequently boosted with a third dose (first booster)