A Study to Learn About a COVID-19 Vaccine in Healthy Adults 50 Through 64 Years of Age

This study is designed to find out how well the COVID-19 vaccine protects people 50 to 64, who don't have any serious health problems, compared to a group that receives a vaccine that doesn't contain an ingredient to protect against COVID-19 (placebo).

Key Inclusion Criteria * People who are between 50 and 64 years old at their first appointment. * People who are healthy and, based on their medical history and a doctor's judgment, are considered suitable to join the study. Key Exclusion Criteria * People who had COVID-19 in the past 3 months (90 days) before their first visit. * People who got a COVID-19 vaccine, either as part of a research study or an approved vaccine, in the last 3 months-or plans to get one during the study.