A Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of mRNA-1283 in Participants ≥6 Months to <12 Years of Age

mRNA-1283 will be administered at 2 different dose levels (Dose Level 1 and Dose Level 2), with mRNA-1273 serving as the active comparator. Dose Level 1 will be the lower dose, and Dose Level 2 will be the higher dose. The study will consist of 2 cohorts. In Cohort 1, mRNA-1283 will be administered as a single dose to participants aged ≥2 to \<12 years, regardless of prior coronavirus disease 2019 (COVID-19) vaccination status, with mRNA-1273 included as a comparator. In Cohort 2, mRNA-1283 will be administered as a 2-dose series to participants aged ≥6 months to \<2 years who are previously unvaccinated for COVID-19, with mRNA-1273 included as a comparator.