Study of Monovalent and Bivalent Recombinant Protein Vaccines Against COVID-19 in Adults 18 Years of Age and Older

The purpose of this Phase III study is to assess the efficacy, safety, and immunogenicity of two CoV2 preS dTM-AS03 vaccines (monovalent and bivalent) as part of primary series vaccinations in a multi-stage approach, as well as a booster injection of a CoV2 preS dTM-AS03 vaccine, in adults 18 years of age and older. A total of approximately 21 046 participants are planned to be enrolled (5080 per study intervention group in Stage 1 and 5443 per study intervention group in Stage 2). Initial, double-blind, primary series study design is planned for 365 days post-last Initial injection (ie, approximately 386 days total) for each participant. Based on decisions of the Study Oversight Group, Stage 1 and Stage 2 participants will be invited to participate in an unblinded Crossover / Booster study design with duration as follows: * For participants who initially received vaccine: 12 months post-booster (ie, approximately 18 to 24 months) * For participants who initially received placebo: ≥ 4 months post-last dose of the primary series + 12 months post-booster (ie, approximately 28 to 34 months) * For participants who do not consent to continue in the unblinded Crossover / Booster part of the study, all study procedures will be stopped and participants will be discontinued from the study.

The duration of participation in the initial, double-blind, primary series design of the study will be approximately 365 days post-last injection (ie, approximately 386 days total) for each participant. Based on decisions of the Study OG, Stage 1 and Stage 2 participants will be invited to participate in an unblinded Crossover / Booster study design with duration as follows: * For participants who initially received vaccine: 12 months post-booster (ie, approximately 18 to 24 months) * For participants who initially received placebo: ≥ 4 months post-last dose of the primary series + 12 months post-booster (ie, approximately 28 to 34 months) * For participants who do not consent to continue in the unblinded Crossover / Booster part of the study, all study procedures will be stopped and participants will be discontinued from the study.