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

Inclusion Criteria

• Age:
• Cohort 1: 18 through 55 years of age.
• Cohort 2: 12 years of age and older.
• Cohort 3: 18 years of age and older.
• Cohort 4: 18 through 55 years of age.
• Willing and able to comply with all scheduled visits/contacts, study procedures and lifestyle considerations.
• Healthy participants (stable pre-existing disease permitted).
• Capable of giving signed informed consent.
• Prior COVID-19 vaccination history:

Cohort 1:

• Received of 1 booster dose of a US-authorized COVID-19 vaccine, with the dose being 90 or more days before first study visit. Documented receipt of all prior COVID-19 vaccines is required.

Cohorts 2 and 3:

• Received 3 prior doses of 30 micrograms BNT162b2, with last dose being 150 to 365 days before first study visit. Documented receipt of all prior COVID-19 vaccines is required.

Cohort 4:

• 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 Omicron BA.4/BA.5-adapted vaccine and dose level at least 150 days before first study visit. Documented receipt of all prior COVID-19 vaccines is required.

Exclusion Criteria

• History of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study vaccines.
• Known or suspected immunodeficiency.
• Bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection.
• Women who are pregnant or breastfeeding.
• Other medical or psychiatric condition, or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.
• Immunosuppressants/radiotherapy:

Cohorts 1 and 2: Receipt of chronic systemic treatment with known immunosuppressant medications (including cytotoxic agents or systemic corticosteroids), or radiotherapy, within 60 days before study vaccination through end of study.

Cohorts 3 and 4: Receipt of chronic systemic treatment with known immunosuppressant medications (including cytotoxic agents or systemic corticosteroids, eg, for cancer or an autoimmune disease), or radiotherapy, within 60 days before enrollment or planned receipt through conclusion of the study.

• Blood/plasma products, immunoglobulin, or monoclonal antibodies:

Cohorts 1, 2, 3: Receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies, from 60 days before study vaccination or planned receipt throughout the study.

Cohort 4: Receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies used for treatment/prevention of COVID-19 or those considered immunosuppressive, from 60 days before study vaccination or planned receipt throughout the study.

• Other study participation:

Cohorts 1 and 2: Participation in other studies involving a study intervention within 28 days before randomization. Anticipated participation in other studies within 28 days after receipt of study intervention in this study.

Cohorts 3 and 4: Participation in other studies involving receipt of a study intervention within 28 days before randomization. Anticipated participation in other studies involving a study intervention from randomization through the end of this study.

• Investigator site staff directly involved in the conduct of the study and their family members, site staff otherwise supervised by the investigator, and sponsor and sponsor delegate employees directly involved in the conduct of the study and their family members.
• Cohort 4 only: History of myocarditis or pericarditis