To evaluate the safety and immunogenicity of the MVA-SIBP vaccine using a double-blind, randomized, controlled, age de-escalation design conducted in Kinshasa, Democratic Republic of the Congo (DRC).

Given the urgent need for pediatric data and the high burden of mpox in the DRC, this trial will evaluate the safety and immunogenicity of the MVA-SIBP vaccine using a double-blind, randomized, controlled, age de-escalation design conducted in Kinshasa, DRC. The trial is designed to generate critical data to support regulatory approval and broader access to affordable, stable, and scalable mpox vaccines for Africa.

Inclusion Criteria:

• Adults: 18 to 45 years inclusive at the time of informed consent. Adolescents: 12 to 17 years inclusive at the time of consent/assent. Children: 2 to 11 years inclusive at the time of consent/assent.
• Participant is in good general health as determined by medical history, targeted physical examination, and clinical judgment of the investigator.
• Adults: Able to read and understand the written informed consent, and willing to comply with all study procedures and availability for the entire study duration. Adolescents: Parent(s) or legally acceptable representative(s) able and willing to provide written informed consent; participant able and willing to provide appropriate assent per local regulations and IRB requirements. Children: Parent(s) or legally acceptable representative(s), with the relationship to the child similarly verified and documented on the consent form, and able and willing to provide written informed consent.
• Willing and able to comply with all study procedures, visit schedule, and follow-up requirements as judged by the investigator.
• No history of smallpox or mpox vaccination. No history of confirmed or suspected infection with monkeypox, cowpox, or vaccinia virus.
• Negative serum or urine pregnancy test at screening and prior to each vaccination. Willing to use highly effective contraception from 30 days prior to first vaccination through 60 days after the last dose. Breastfeeding.
• Resides in the study catchment area and has no plans to relocate for the duration of the study. Has reliable access to a telephone and/or other means of contact.
• Adults must have been born in 1980 or later. Able to provide direct written informed consent.
• Adolescents: Able to provide written or written assent as appropriate. Children: Parent(s)/guardian(s) able to provide written informed consent; child able to provide assent if developmentally appropriate.

Exclusion Criteria:

• Any prior smallpox or mpox vaccination. History of confirmed or suspected infection with monkeypox, cowpox, or vaccinia virus.
• Close contact, as defined by WHO.
• Known or suspected immunocompromised state as specified in the protocol.
• Acute febrile illness (≥38.0°C) or clinically significant infection within 72 hours prior to vaccination. Any acute illness requiring systemic therapy or hospitalization within 14 days prior to enrollment.
• History of severe allergy or anaphylaxis to any vaccine or vaccine component. History of severe allergic asthma or asthmatic reactions.
• Pregnant or breastfeeding at screening or planning to become pregnant during the study period.
• Participation in another clinical trial with an investigational product or vaccine within 6 months prior to enrollment or planned during the study.
• Receipt of any live vaccine within 28 days or inactivated vaccine within 14 days prior to enrollment or planned within 28 days after any study vaccination.
• Any medical disease or condition that, in the opinion of the investigator, would place the participant at unacceptable risk, interfere with study objectives, or compromise protocol compliance.
• Blood transfusion within three months before inclusion. Significant laboratory test result abnormalities should be added as exclusion criteria. Any condition that, in the opinion of the investigator, would preclude safe participation or successful completion of the study.