The main objective of Part A of this trial is to evaluate the safety and reactogenicity of mRNA-1189 in 18- to 30-year-old healthy adults, the main objective of Part B is to evaluate the safety and reactogenicity of mRNA-1189 in 12- to \<18-year-old healthy EBV-seronegative adolescents, and the main objective of Part C is to evaluate the safety and reactogenicity of mRNA-1189 in 10- to 21-year-old healthy adolescents and adults.