Participants must meet all inclusion criteria to be eligible for the study. ALL PARTICIPANTS: 1. Participants of either gender aged 18 years and older at screening 2. Participants must have read, understood, and signed the informed consent form (ICF) 3. Medically stable such that, according to the judgment of the investigator, hospitalization within the study period is not anticipated and the participant appears likely to be able to remain on study through the end of protocol-specified follow-up. 4. Participant has a Body Mass Index (BMI) of 18.0-30.0 kg/m2, inclusive, at screening (Visit 0). 5. Must be able to attend all visits of the study and comply with all study procedures, including daily completion of the e-diary for 7 days following each vaccination. 6. Women of childbearing potential (WOCBP), who are sexually active with a man, must be able and willing to use at least 1 highly effective method of contraception (i.e. implant contraceptive, intra-uterine device (IUD) containing either copper or levonorgestrel, male sterilization [vasectomy], female sterilization, injectable contraceptive, oral contraceptive pill, vaginal contraceptive ring, barrier type of birth control measure) from study start until a minimum of 3 months after receiving the booster vaccine. 7. WOCBPs must have a negative pregnancy test prior to the booster vaccination. Only applicable for Cohort “mRNA primed”: 8. Has received a second dose of licensed mRNA COVID-19 vaccine 6 to 12 months before study vaccination Only applicable for Cohort “naturally primed”: 9. PCR confirmed natural SARS-CoV-2 infection 6 to 12 months before study vaccination

Participants must meet all inclusion criteria to be eligible for the study. ALL PARTICIPANTS: 1. Participants of either gender aged 18 years and older at screening 2. Participants must have read, understood, and signed the informed consent form (ICF) 3. Medically stable such that, according to the judgment of the investigator, hospitalization within the study period is not anticipated and the participant appears likely to be able to remain on study through the end of protocol-specified follow-up. 4. Participant has a Body Mass Index (BMI) of 18.0-30.0 kg/m2, inclusive, at screening (Visit 0). 5. Must be able to attend all visits of the study and comply with all study procedures, including daily completion of the e-diary for 7 days following each vaccination. 6. Women of childbearing potential (WOCBP), who are sexually active with a man, must be able and willing to use at least 1 highly effective method of contraception (i.e. implant contraceptive, intra-uterine device (IUD) containing either copper or levonorgestrel, male sterilization [vasectomy], female sterilization, injectable contraceptive, oral contraceptive pill, vaginal contraceptive ring, barrier type of birth control measure) from study start until a minimum of 3 months after receiving the booster vaccine. 7. WOCBPs must have a negative pregnancy test prior to the booster vaccination. Only applicable for Cohort “mRNA primed”: 8. Has received a second dose of licensed mRNA COVID-19 vaccine 6 to 12 months before study vaccination Only applicable for Cohort “naturally primed”: 9. PCR confirmed natural SARS-CoV-2 infection 6 to 12 months before study vaccination