- Male or female participants between the ages of 18 and 30 years, inclusive at randomization.- Healthy participants who are determined by medical history and clinical judgment of the investigator to be eligible for inclusion in the study. Healthy participants with preexisting stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 6 weeks before enrolment, can be included.- Participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures.- Capable of giving personal signed informed consent as described in Appendix 1, which includes compliance with the requirements and restrictions listed in the ICD and in this protocol.- Females only: female volunteers of childbearing potential (i.e. have a uterus and are neither surgically sterilized nor postmenopausal) must not be pregnant or breastfeeding. They should agree to use adequate contraception at least up to four weeks following the final dose of mRNA-1273 vaccine

- Male or female participants between the ages of 18 and 30 years, inclusive at randomization.- Healthy participants who are determined by medical history and clinical judgment of the investigator to be eligible for inclusion in the study. Healthy participants with preexisting stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 6 weeks before enrolment, can be included.- Participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures.- Capable of giving personal signed informed consent as described in Appendix 1, which includes compliance with the requirements and restrictions listed in the ICD and in this protocol.- Females only: female volunteers of childbearing potential (i.e. have a uterus and are neither surgically sterilized nor postmenopausal) must not be pregnant or breastfeeding. They should agree to use adequate contraception at least up to four weeks following the final dose of mRNA-1273 vaccine