A Study to Evaluate the Immunogenicity and Safety of mRNA Vaccine Boosters for SARS-CoV-2 (COVID-19) Variants

This clinical study will consist of 9 parts: A (1 and 2), B, C, D, E, F, G, H, and J. Part A.1 will evaluate 2 dose levels of the mRNA-1273.211 vaccine when administered as a single booster dose to adult participants of the mRNA-1273-P301 (COVE \[NCT04470427\]) study who have previously received 2 doses of mRNA-1273. Part A.2 will evaluate the immunogenicity, safety, and reactogenicity of the mRNA-1273.214 vaccine candidate when administered as a second booster dose to adult participants of the mRNA-1273-P205 study who have previously received 2 doses of mRNA-1273 as a primary series and a first booster of (50 μg total mRNA content) of the mRNA-1273.211 in Part A.1 of this study. Part B will evaluate the mRNA-1273 vaccine when administered as a single booster dose to adult participants of the mRNA-1273-P301 (COVE \[NCT04470427\]) study who have previously received 2 doses of mRNA-1273. Part C will evaluate 2 dose levels of the mRNA-1273.617.2 vaccine when administered as a single booster dose to adult participants of the mRNA-1273-P301 (COVE \[NCT04470427\]) study who have previously received 2 doses of mRNA-1273. Part D will evaluate 2 dose levels of the mRNA-1273.213 vaccine when administered as a single booster dose to adult participants of the mRNA-1273-P301 (COVE \[NCT04470427\]) study who have previously received 2 doses of mRNA-1273. Part E will be enrolled at a single clinical study site. Part E will evaluate the mRNA-1273.213 vaccine when administered as a single booster dose to adult participants who have previously received 2 doses of any SARS-CoV-2 mRNA authorized vaccine, including mRNA-1273. Part F will consist of 2 cohorts: Cohort 1 will consist of adults who have previously received 2 doses of mRNA-1273 as primary series. Cohort 1 will evaluate the mRNA-1273.529 vaccine as a single booster dose. Cohort 2 will consist of adults who have previously received 2 doses of mRNA-1273 as a primary series and a single booster dose of mRNA-1273 in study mRNA-1273-P301 (COVE \[NCT04470427\]) or under the emergency use authorization (EUA). Cohort 2 will evaluate the mRNA-1273.529 and mRNA-1273 vaccines as a single booster dose. Part G will evaluate the mRNA1273.214 vaccine candidate when administered as a second booster dose to adults who have previously received 2 doses of mRNA-1273 as a primary series and a single booster dose of mRNA-1273. Part H will evaluate the immunogenicity, safety, and reactogenicity of the mRNA- 1273.222 vaccine candidate when administered as a second booster dose to adults who have previously received 2 doses of mRNA-1273 as a primary series and a single booster dose of mRNA-1273. Part J will evaluate mRNA-1273.815 and mRNA-1273.231 when administered as a booster dose to adults who previously received a primary series of mRNA vaccine, a first booster dose of a monovalent mRNA vaccine, and a second booster dose of a bivalent mRNA vaccine against SARS-COV-2.