The goal of this observational study is to monitor and assess the safety profile of the MVA-BN vaccine among staff and study personnel of the PALM-007 study in the Democratic Republic of the Congo. The main questions it aims to answer are:

• To estimate the incidence of serious adverse events (SAEs) in all individuals vaccinated with the MVA-BN vaccine
• To estimate the incidence of adverse events (AEs) after each dose of MVA-BN vaccine.

Participants will receive two doses of vaccine and will be actively followed up to the 28th day after their last dose of MVA-BN vaccine.

All personnel and staff of the PALM-007 study will be offered the opportunity to participate in the study by reviewing and signing the informed consent. After signing informed consent, participants will be examined. The following parameters will be assessed:

• Anthropometric measurements (weight, height)
• Vital signs: temperature (axillary), blood pressure, heart rate and respiratory rate
• Medical history, including history of orthopox virus disease, vaccination, current co-morbidities and medication(s)
• Physical examination
• Pregnancy test will be done for all women of childbearing potential

If a participant has met all eligibility criteria, they will be enrolled and will receive the vaccine as specified below. Participants who are excluded because of fever can be rescreened and included after resolution of the fever and its cause.

Enrolled participants will receive the MVA-BN vaccine by subcutaneous injection of 0.5 mL in the shoulder (left or right).

The first dose will be administered at the time of enrollment and the second dose 28 days later.

After each vaccination, the participant will remain under observation for 30 minutes. All AEs occurring during this period of observation will be recorded and reported to the National Center for Pharmacovigilance and to the ethics committee according to Congolese regulations.

Follow-up of participants:

Participants will be followed until 28 days after the second dose of vaccine. Follow-up visit will be done either in person at National Institute of Biomedical Research (INRB) in Kinshasa and at the Monkeypox treatment centers in the PALM-007 study or by phone calls on Day 3, Day 14, and Day 28 post each vaccination. Study participants will be provided with contact information of vaccine research staff and have the right to contact the research team either directly or by phone if they have any questions about post-vaccination reactions they may be experiencing or if they are concerned. There is a window of +/- one day for each study visit except the day of the second dose which can be done on day 28 after the first dose with a window of +7 days. This second dose must not be given before Day 28. During each visit, participants will be asked to report to the research team AEs via open-ended questions. All SAEs will be followed-up. SAEs that have not resolved by the end of the per-protocol follow-up period for the subject (Day 28 after second dose) are to be followed until final outcome is known (to the degree permitted by the IRB-approved informed consent form). If it is not possible to obtain a final outcome for an SAE (e.g., the participant is lost to follow-up), the last known status and the reason a final outcome could not be obtained will be recorded by the investigator on an SAE report update and the CRF.

On the day of administration of the second dose of vaccine, vital signs, and physical examination will be done to all participants and a pregnancy test will be done on all women of childbearing potential prior to vaccine administration. If the pregnancy test is positive, the second dose will not be given, and the participant will be followed up as described in the protocol. Participants will be instructed to report any AEs that are experienced outside of the protocol defined follow up days. The reporting form of the national pharmacovigilance system of the DRC will be used for reporting. The research team will complete the notification form which will be sent to the National Pharmacovigilance Center (CNPV) by e-mail (scanned copies).

Inclusion Criteria:

• Provides written informed consent
• 18 years of age or older
• At high risk for Monkeypox infections
• Personnel and staff associated with the PALM 007-Monkeypox study sites in the DRC
• Willingness and ability to communicate AEs to study personnel

Exclusion Criteria:

• Allergy to MVA-BN or any of its components
• Pregnant or breastfeeding women
• Fever (axillary temperature ≥37.5°celsius)
• People who have already received the MVA-BN vaccine (in routine vaccination or another study involving this vaccine)
• Participants who, in the judgement of the investigator, will be at significantly increased risk as a result of participation in the study
• Individuals with any condition or circumstance that would render them unable to comply with study procedures (e.g., not reachable by phone)

From enrollment until the end of follow-up, up to 28 days after receipt of the second vaccine dose