Medically attended AEs were defined as AEs with medically attended visits that are not routine visits for physical examination or vaccination, such as visits for hospitalization, an emergency room visit, or an otherwise unscheduled visit to or from medical personnel (medical doctor) for any reason. The Investigator assessed the relationship between trial vaccine and occurrence of each AE.

An SAE was defined as any untoward medical occurrence that, at any dose: * Resulted in death. * Was life-threatening. * Required inpatient hospitalization or prolongation of existing hospitalization. * Resulted in persistent disability/incapacity. * Was a congenital anomaly/birth defect in the offspring of the participant. * Was an important medical event. The Investigator assessed the relationship between trial vaccine and occurrence of each AE.

An SAE was defined as any untoward medical occurrence that, at any dose: * Resulted in death. * Was life-threatening. * Required inpatient hospitalization or prolongation of existing hospitalization. * Resulted in persistent disability/incapacity. * Was a congenital anomaly/birth defect in the offspring of the participant. * Was an important medical event. The Investigator made an assessment of intensity for each AE reported during the trial and assigned it to one of the following categories: * Mild: an event that was easily tolerated by the participant, causing minimal discomfort and not interfering with everyday activities. * Moderate: an event that caused sufficient discomfort to interfere with normal everyday activities. * Severe: an event that prevented normal everyday activities.

The following events were considered and collected as AESI throughout the trial: * AEs with a suspected immune-mediated etiology. * Other AEs relevant to SARS-CoV-2 vaccine development or the target disease. * COVID-19. The Investigator assessed the relationship between trial vaccine and occurrence of each AE.

An SAE was defined as any untoward medical occurrence that, at any dose: * Resulted in death. * Was life-threatening. * Required inpatient hospitalization or prolongation of existing hospitalization. * Resulted in persistent disability/incapacity. * Was a congenital anomaly/birth defect in the offspring of the participant. * Was an important medical event.

eDiaries were used for the collection of unsolicited AEs on each vaccination day and the following 28 days. The Investigator assessed the relationship between trial vaccine and occurrence of each AE.

eDiaries were used for the collection of unsolicited AEs on each vaccination day and the following 28 days. The Investigator made an assessment of intensity for each AE reported during the trial and assigned it to one of the following categories: * Mild: an event that was easily tolerated by the participant, causing minimal discomfort and not interfering with everyday activities. * Moderate: an event that caused sufficient discomfort to interfere with normal everyday activities. * Severe: an event that prevented normal everyday activities.

Titers of IgG antibodies directed against the SARS-CoV-2 RBD of Spike Protein antigen were measured by enzyme-linked immunosorbent assay (ELISA). Percentage with 95% confidence interval (CI) of participants for whom a seroconversion was observed is presented by group. Seroconversion was defined as a fold increase above 1 in SARS-CoV-2 Spike Protein RBD IgG antibody levels in participants seronegative at Baseline. Participants who tested positive for COVID-19 had their data included up to the point of a positive test result. Participants who received a licensed/authorized vaccine were censored at the day after receiving the licensed/authorized vaccine.

Titers of IgG antibodies directed against the SARS-CoV-2 RBD of Spike Protein antigen were measured by ELISA and expressed as geometric mean of titers (GMT) with 95% CI, by group. Individual values below the lower limit of quantification (LLOQ) were set to half of the LLOQ. Participants who tested positive for COVID-19 had their data included up to the point of a positive test result. Participants who received a licensed/authorized vaccine were censored at the day after receiving the licensed/authorized vaccine.