Geometric Mean (GM) of the Serum Ab Level;GM of the Serum Ab Level of Original Strain Post BD;Number of Participants with AEs Leading to the Discontinuation From Study Post BD;Number of Participants with Serious Adverse Events (SAEs), Medically Attended AEs (MAAEs), or Adverse Events of Special Interest (AESI);Number of Participants With Serum Antibody (Ab) Levels that Meet or Exceed the Threshold of Protection From COVID-19;Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs);Number of Participants with Unsolicited Adverse Events (AEs);Seroresponse Rate (SRR) of Vaccine Recipients;SRR of Vaccine Recipients of Original Strain Post BD

Geometric Mean (GM) of the Serum Ab Level;GM of the Serum Ab Level of Original Strain Post BD;Number of Participants with AEs Leading to the Discontinuation From Study Post BD;Number of Participants with Serious Adverse Events (SAEs), Medically Attended AEs (MAAEs), or Adverse Events of Special Interest (AESI);Number of Participants With Serum Antibody (Ab) Levels that Meet or Exceed the Threshold of Protection From COVID-19;Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs);Number of Participants with Unsolicited Adverse Events (AEs);Seroresponse Rate (SRR) of Vaccine Recipients;SRR of Vaccine Recipients of Original Strain Post BD

Part A and C: Number of Participants with Serious Adverse Events (SAEs), Medically Attended AEs (MAAEs), or Adverse Events of Special Interest (AESI);Part A and C: Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs);Part A and C: Number of Participants with Unsolicited Adverse Events (AEs);Part A: Geometric Mean (GM) of the Serum Ab Level;Part A: Number of Participants With Serum Antibody (Ab) Levels that Meet or Exceed the Threshold of Protection From COVID-19;Part A: Seroresponse Rate (SRR) of Vaccine Recipients;Part C: GM of the Serum Ab Level of Original Strain Post BD;Part C: Number of Participants with AEs Leading to the Discontinuation From Study Post BD;Part C: SRR of Vaccine Recipients of Original Strain Post BD

Part A and C: Number of Participants with Serious Adverse Events (SAEs), Medically Attended AEs (MAAEs), or Adverse Events of Special Interest (AESI);Part A and C: Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs);Part A and C: Number of Participants with Unsolicited Adverse Events (AEs);Part A: Geometric Mean (GM) of the Serum Ab Level;Part A: Number of Participants With Serum Antibody (Ab) Levels that Meet or Exceed the Threshold of Protection From COVID-19;Part A: Seroresponse Rate (SRR) of Vaccine Recipients;Part C: GM of the Serum Ab Level of Original Strain Post BD;Part C: Number of Participants with AEs Leading to the Discontinuation From Study Post BD;Part C: SRR of Vaccine Recipients of Original Strain Post BD

Geometric Mean (GM) of the Serum Ab Level;Number of Participants with Serious Adverse Events (SAEs), Medically Attended AEs (MAAEs), or Adverse Events of Special Interest (AESI) of Multisystem Inflammatory Syndrome in Children (MIS-C);Number of Participants With Serum Antibody (Ab) Levels that Meet or Exceed the Threshold of Protection From COVID-19;Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs);Number of Participants with Unsolicited Adverse Events (AEs);Seroresponse Rate of Vaccine Recipients

Geometric Mean (GM) of the Serum Ab Level;Number of Participants with Serious Adverse Events (SAEs), Medically Attended AEs (MAAEs), or Adverse Events of Special Interest (AESI) of Multisystem Inflammatory Syndrome in Children (MIS-C);Number of Participants With Serum Antibody (Ab) Levels that Meet or Exceed the Threshold of Protection From COVID-19;Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs);Number of Participants with Unsolicited Adverse Events (AEs);Seroresponse Rate of Vaccine Recipients

Comparison of the Geometric Mean of the Serum Neutralizing Antibody (nAb) level against the Geometric Mean of the Serum nAb level in Study mRNA-1273-P301 (NCT04470427);Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs);Number of Participants with Unsolicited Adverse Events (AEs);Number of Participants with Serious Adverse Events (SAEs), Medically Attended AEs (MAAEs), or Adverse Events of Special Interest (AESI);Number of Participants Who have Reached the Acceptable Threshold for the Serum Ab Level at Day 57

Comparison of the Geometric Mean of the Serum Neutralizing Antibody (nAb) level against the Geometric Mean of the Serum nAb level in Study mRNA-1273-P301 (NCT04470427);Number of Participants with Solicited Local and Systemic Adverse Reactions (ARs);Number of Participants with Unsolicited Adverse Events (AEs);Number of Participants with Serious Adverse Events (SAEs), Medically Attended AEs (MAAEs), or Adverse Events of Special Interest (AESI);Number of Participants Who have Reached the Acceptable Threshold for the Serum Ab Level at Day 57