A Randomized Clinical Trial Investigating the Safety, Reactogenicity, and Immunogenicity After Immunization With an mRNA-based Mpox Vaccine Candidate in Africa

Key Inclusion Criteria (applicable to all participants unless otherwise specified): * Are male or female individuals ≥18 years of age at the time of giving informed consent: * Cohort 1: ≥18 to ≤45 years of age * Cohort 2: ≥18 to ≤64 years of age * Cohort 1: Participants must be Orthopoxvirus-naïve (have no history of smallpox or mpox vaccination or mpox infection). * Cohort 2: Participants must be Orthopoxvirus-experienced (have evidence of mpox or smallpox vaccination or mpox infection at least 2 years prior to consent). Key Exclusion Criteria (applicable to all participants unless otherwise specified): * Have had recent exposure to mpox (defined as close contact with a probable or confirmed case of mpox within the past 28 days, or have evidence of mpox infection or mpox vaccination within 2 years prior to consent). * Have a contraindication, warning and/or precaution to vaccination with a messenger ribonucleic acid (mRNA) Coronavirus disease 2019 (COVID-19) vaccine as specified in the Summary of Product Characteristics for BNT162b2 (COMIRNATY United States Prescribing Information/European Union Summary of Product Characteristics) and BNT166 Investigator Brochure. * Have a history of allergies, hypersensitivities, or intolerance to the study treatments including any excipients thereof. * Have a current or history of cardiovascular diseases, e.g., myocarditis, pericarditis, myocardial infarction, congestive heart failure, cardiomyopathy, or clinically significant arrhythmias. * Have any known bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. * Have a body mass index ≤18.5 kg/m\^2 or ≥35 kg/m\^2. NOTE: Other protocol defined Inclusion/Exclusion criteria apply.