A Study to Learn About New COVID-19 RNA Vaccine Candidates in COVID-19 Vaccine-Experienced Healthy Individuals

Protocol summary

The purpose of this clinical trial is to learn about the safety, tolerability and immunogenicity of BNT162b RNA-based SARS-CoV-2 vaccine candidates in adults to prevent COVID-19. For all cohorts (groups of participants), this study is seeking participants who are healthy (who may have preexisting disease if it is stable); All participants will receive a single dose of the study vaccine at the first study clinic and will return to the study clinic at least 4 more times. At each clinic visit, a blood sample will be taken. The study is about 6 months long for each participant. The vaccine candidates in this study are investigational but are very similar to BNT162b2 (Comirnaty), a COVID-19 RNA vaccine approved for use in the US and in many countries. For Cohort 1, this study included participants who were: * 18 through 55 years of age * have received 1 booster dose of a US-authorized COVID-19 vaccine, with the last dose being 90 or more days before Visit 1 of this study. All participants in Cohort 1 will receive 1 of the 2 study vaccines at a 30 microgram dose: BNT162b5 Bivalent (WT/OMI BA.2) or BNT162b2 Bivalent (WT/OMI BA.1). For Cohort 2, this study included participants who were: * 12 years of age and older * have received 3 prior doses of 30 micrograms BNT162b2, with the last dose being 150 to 365 days before Visit 1 of this study. Participants 12 through 17 years of age will receive BNT162b2 Bivalent (WT/OMI BA.4/BA.5) 30 micrograms. Participants 18 years and older will receive BNT162b2 Bivalent (WT/OMI BA.4/BA.5) at either a 30 microgram or a 60 microgram dose. For Cohort 3, this study included participants who were: * 18 years of age and older * have received 3 prior doses of 30 micrograms BNT162b2, with the last dose being 150 to 365 days before Visit 1 of this study. * Participants will receive BNT162b2 Bivalent (WT/OMI BA.4/BA.5) 30 micrograms. For Cohort 4, this study is seeking participants who are: * 18 through 55 years of age * have received 3 or 4 prior doses of a US-authorized mRNA COVID-19 vaccine (and dose level), with the last dose being a US-authorized BA.4/BA.5-adapted bivalent vaccine and dose level at least 150 days before Visit 1 of this study. All participants in Cohort 4 will receive 1 of the 5 study vaccines at a 30 microgram dose: BNT162b2 Bivalent (Original/ OMI BA.4/BA.5), BNT162b5 Bivalent (Original/OMI BA.4/BA.5), BNT162b6 Bivalent (Original/OMI BA.4/BA.5), BNT162b7 Bivalent (Original/OMI BA.4/BA.5) or BNT162b7 Monovalent (OMI BA.4/BA.5).