A Study to Learn About New COVD-19 RNA Vaccine Candidates for New Variants in Healthy Individuals

SSA Inclusion Criteria: Received at least 3 prior doses of a US-authorized mRNA COVID-19 vaccine, with the most recent dose being a US-authorized Omicron BA.4/BA.5-adapted bivalent vaccine received at least 150 days before Visit 1 (Day 1). 12 years of age and older Healthy participants (stable pre-existing disease permitted). Willing and able to comply with all scheduled visits/contacts, study procedures and lifestyle considerations. Capable of giving, or parent(s)/legal guardian capable of giving, signed informed consent. 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. Immunocompromised with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination. 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. Any 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. History of myocarditis or pericarditis. Receipt of 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. Receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies, used for the treatment or prevention of COVID-19 or those that are considered immunosuppressive, from 60 days before study vaccination or planned receipt throughout the study. Participation in other studies involving receipt of other study intervention within 28 days before enrollment. Anticipated participation in other studies involving other study intervention from enrollment 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. SSB Inclusion Criteria: COVID-19 vaccine-naïve. Any positive SARS-CoV-2 test result >28 days before study intervention administration. 12 years of age and older. Healthy participants (stable pre-existing disease permitted). Willing and able to comply with all scheduled visits/contacts, study procedures and lifestyle considerations. Capable of giving or parent(s)/legal guardian capable of giving, signed informed consent. 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. Immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination. 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. Any medical or psychiatric condition, including recent (within the past year) or active suicidal ideation/behavior, or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. History of myocarditis or pericarditis. Receipt of 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. Receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies used for the treatment or prevention of COVID-19 or those that are considered immunosuppressive, from 60 days before study intervention administration or planned receipt throughout the study. Participation in other studies involving receipt of other study intervention within 28 days before enrollment. Anticipated participation in other studies involving other study intervention from enrollment 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.