A Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of Cytomegalovirus (CMV) Vaccine mRNA-1647

Inclusion Criteria: * Participant is a Japanese Adult 18-40 years of age at the time of consent who, in the opinion of the investigator, is in good health based on review of medical history and screening physical examination. Japanese participants are defined as individuals born in Japan, with both parents and 4 grandparents who were born in Japan, and who have not lived outside of Japan for more than 10 years in total. * For the CMV-seronegative groups: Participant is serum CMV IgG negative/ IgM negative. * For the CMV-seropositive groups: Participant is either serum CMV IgG positive/IgM negative or IgG positive/IgM positive. * Participant has a body mass index (BMI) from ≥18 kilograms (kg)/square meter (m\^2) to ≤35 kg/m\^2, inclusive. Exclusion Criteria: * History of a diagnosis or condition that, in the judgment of the investigator, is clinically unstable or may affect participant safety, assessment of safety endpoints, assessment of immune response, or adherence to study procedures. Clinically unstable is defined as a diagnosis or condition requiring significant changes in management or medication within the 2 months prior to screening and includes ongoing workup of an undiagnosed illness that could lead to a new diagnosis or condition. * Participant has elevated liver function tests, defined as aspartate aminotransferase (AST), alanine aminotransferase (ALT), or alkaline phosphatase (ALP), or elevated creatinine or reduced platelets, with a toxicity score of Grade ≥1…