Dose-Finding Trial to Evaluate the Safety and Immunogenicity of Cytomegalovirus (CMV) Vaccine mRNA-1647 in Healthy Adults

Inclusion Criteria: * Male or female 18-40 years of age (Part 1); Female 18-40 years of age (Part 2) * Understands and agrees to comply with the trial procedures and provides written informed consent * According to the assessment of the Investigator, is in good general health and is capable of complying with trial procedures * Body mass index (BMI) 18-35 kilograms/meter (kg/m\^2) * Female participants must either be of non-childbearing potential or use acceptable methods of contraception from at least 28 days prior to the first vaccination and through 3 months following last vaccination and is not breastfeeding. * Male participants must agree to practice adequate contraception from the time of the first vaccination and through 3 months after the last vaccination. Exclusion Criteria: * Acutely ill or febrile on the day of the first vaccination * Prior receipt of any CMV vaccine * Abnormal screening safety laboratory test results * Diagnosis or condition that, in the judgment of Investigator, is clinically unstable or may affect participant safety, assessment of safety endpoints, assessment of immune response, or adherence to trial procedures * Has received or plans to receive a vaccine ≤28 days prior to the first vaccination or plans to receive a non-study vaccine within 28 days prior to or after any study vaccination, except for any licensed influenza vaccine which can be administered \>14 days before or after any study vaccination. COVID-19 vaccines (regardless of manufac…