A Clinical Study Investigating the Safety and Immune Responses After Immunization With Investigational Monkeypox Vaccines

Inclusion Criteria (applicable to all substudies unless otherwise specified): * Have given informed consent by signing and dating the informed consent form (ICF) before initiation of any study-specific procedures. * Are willing and able to comply with scheduled visits, treatment schedule, laboratory tests, and other requirements of the study, including the prohibited concomitant medications. This includes that they are able to understand and follow study-related instructions. * SSA and SSD only: Are 18 through 45 years of age (inclusive) at the time of informed consent. * SSB only: Are 50 through 65 years of age (inclusive) at the time of informed consent. * Have a body mass index over 18.5 kg/m\^2 and under 30 kg/m\^2 and weigh at least 50 kg at Visit 0. * Are healthy, in the clinical judgment of the investigator based on volunteer-reported medical history data, physical examination, 12-lead electrocardiogram (ECG), vital signs, and clinical laboratory test results. * SSA and SSD only: Have no prior history of known or suspected smallpox vaccination and no detectable smallpox vaccination characteristic scar (vaccinia-naïve participants). * SSB only: Have a history of prior smallpox vaccination (i.e., are vaccinia-experienced), determined based on medical records and/or presence of smallpox vaccination characteristic scar. The most recent smallpox vaccination should have been received before 1980. * Agree not to enroll in another study with an investigational medicinal produ…