A Study of SARS CoV-2 Infection and Potential Transmission in Individuals Immunized With Moderna COVID-19 Vaccine

This study will evaluate the efficacy of the Moderna COVID-19 vaccine against SARS-CoV-2 infection, as well as its effect on peak nasal viral load as a measure of infection and a proxy of infectiousness, in adults aged 18-29. In the Main study, up to 12,000 participants will be randomized 1:1 to Immediate Vaccination Group 1 (at Months 0 and 1) or Standard of Care Group 2, with vaccination given at Months 4 and 5 if not received off-study previously. Up to an additional 6,000 participants will be enrolled into the Vaccine Declined Group 3 and will also be offered vaccine at Months 4 and 5. Additional study visits for Group 1 will occur at Months 2 and 4; for Groups 2 and 3, at Months 0 and 2. Study visits may include medical history, vaccine injections, blood collection, nasal swab, SARS-CoV-2 screening, COVID-19 symptom check, and questionnaires. In addition to the main study participants, the study will also evaluate infectiousness following close contacts with main study participants. Study procedures for close contacts include questionnaires and blood samples; for those who become SARS-CoV-2 infected, study procedures will also include nasal swabs.