A Study of S-268019 for the Prevention of COVID-19

A Phase 3, Randomized, Observer-Blind, Placebo- Controlled Cross-over Study to Evaluate the Efficacy, Safety, and Immunogenicity of S-268019 for the Prevention of COVID-19

The main purpose of this study is to assess the efficacy of S-268019-b for the prevention of COVID-19 in the initial vaccination period prior to crossover in participants without evidence of infection before vaccination as compared to placebo.

Eligible participants will be randomized to receive either S-268019-b or placebo first and then will be crossed over to receive the opposite intervention. The study will consist of two treatment periods, an initial vaccination period (Day 1 to Day 224), and a crossover vaccination period (Day 225 to Day 435).

Inclusion Criteria:

• Agree not to participate in any other SARS-CoV-2 prevention trial during the study follow-up.
• Capable of using Diary without difficulties (if applicable, with assistance by caregiver).

Exclusion Criteria:

• Current or history of a laboratory-confirmed diagnosis of SARS-CoV-2 infection or COVID-19.
• Unstable current cardiovascular, respiratory, hepatic, renal, gastrointestinal, endocrine, hematological, or neurological disease that, in the opinion of the investigator or subinvestigator, would constitute a safety concern or confound data interpretation.
• Immunosuppression (immunodeficiency, acquired immunodeficiency syndrome [AIDS], use of systemic steroids, use of immunosuppressants within the past 6 months prior to the first dose of study intervention, treatment for malignant tumors, other immunosuppressive therapy).
• Previous vaccination against SARS-CoV-2.
• Any inactivated vaccine received within 14 days prior to the first dose of study intervention.
• Any live vaccine received within 28 days prior to the first dose of study intervention.
• Immunoglobulin preparations, blood products, or a blood transfusion within 3 months prior to the first dose of study intervention.

Other inclusion and exclusion criteria may apply.