The primary objectives of this Phase 1/2 study are:

To describe the safety profile of all participants in each age group and each study intervention group up to 12 months post-last dose.

To describe the neutralizing antibody profile at Day 1, Day 22, and Day 36 of each study intervention group.

The secondary objectives of the study are:

To describe binding antibody profile from Day 1 to Day 387 of each study intervention group.

To describe the neutralizing antibody profile from Day 90 to Day 387 of each study intervention group.

To describe the occurrence of virologically-confirmed COVID-19-like illness and serologically-confirmed SARS-CoV-2 infection.

To evaluate the correlation/association between antibody responses to SARS-CoV-2 mRNA vaccine and the risk of virologically-confirmed COVID-19-like illness and/or serologically-confirmed SARS-CoV-2 infection.