The purpose of this clinical trial is to learn about the safety, extent of the side effects, and immune responses of the study vaccine (called bivalent BNT162b2 Omicron containing vaccine) in healthy children. The trial is divided into 4 individual studies or substudies based on age group and prior history of COVID-19 vaccinations. All participants in each of the 4 sub-studies study vaccine as a shot depending on what group they are in.
- Substudy A design: includes participants 6 months through less than 4 years 3 months of age who have not received a previous coronavirus vaccination (COVID-19 vaccine naïve) and will receive 3 doses of study vaccine as their initial which may be followed by a fourth dose of study vaccine.
- Substudy B design: includes 6 months through less than 5 years of age who have either received 2 or 3 prior doses of BNT162b2 and will receive study vaccine as their third or fourth dose.
- Substudy D design: includes participants 5 through less than12 years of age who have received 2 or 3 prior doses of BNT162b2 and will receive study vaccine as their third or fourth dose.