This Phase 3 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 university students aged 18-26.

Participants will be randomly assigned to 1 of 2 groups. Participants in Group 1 will receive the Moderna COVID-19 vaccine by injection at Months 0 and 1; participants in Group 2 will receive the Moderna COVID-19 vaccine by injection at Months 4 and 5.

Additional study visits for Group 1 will occur at Months 2 and 4; for Group 2, 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.