Inclusion Criteria:
1. The participant must be between 16 and 35 years of age inclusive on the consent day.
2. The participant must pass (≥9/10) the Test of Understanding after being advised of the risks and benefits of the trial in a language understood by the participant and before performing any trial-specific procedures.
* Note: For participants 16-17 years old, the parent/legal guardian must also pass the test of understanding.
* Note: If the participant or parent/legal guardian for 16-17-year-olds fails the TOU test on the first attempt, he/she must be retrained on the purpose of the study and must take the test again (2 repeats are allowed). If participants or their parent/legal guardian fail on the third attempt, they should not continue with screening or consenting procedures.
* Note: Maternal Group 3 participants are not restricted to 3 attempts to pass the TOU. For ethical reasons, these participants will be offered unlimited attempts.
3. The participant must sign and date an informed consent form (≥18 years old) or assent form (16-17 years old) indicating that he or she understands the purpose of and procedures required for the study and is willing to participate in the study.
* Note: If the participant is under 18 years of age, informed consent must also be obtained from a parent/legal guardian capable of providing consent. The consent form must be signed and dated by the parent/guardian after they have read and understood the risks and benefits of the trial and before any trial-specific procedures are performed.
* Note: The partner (father of the child) or guardian for the follow-up of the infant after delivery) must also sign an informed consent/assent form (ICF) indicating that they understand the purpose of, and procedures required for, the study and is willing for their child to participate in the study.
* Note: In case the participant, partner, parent/legal guardian cannot read or write, the procedures must be explained in the presence of an impartial (i.e. not involved in the study) third party witness, and informed consent must be obtained from this impartial third party witness.
4. The participant must be in her second (13-27 weeks) or early third trimester (28-32 weeks) of pregnancy at the time of vaccination.
\- Note: Mpox-infected and exposed pregnant women (Maternal group 3) can enrol at any stage of the pregnancy.
\- Note: Depending on enrolment progress of pregnant women between 13 and 32 weeks gestation, pregnant women in their first trimester may be enrolled but will not be vaccinated until they reach 13 weeks gestation. Sponsor approval needs to be sought to start enrolling pregnant women earlier than 13 weeks gestation.
5. The participant and her unborn child must be generally healthy in the investigator's clinical judgment and on the basis of vital signs assessed at day 1 screening with no severe (chronic) conditions (as far as medically known) that might interfere with vaccine assessment.
\- Note: HIV-positive subjects can be enrolled as long as their general condition is good, i.e., HIV infection under stable Highly Active Antiretroviral Therapy (HAART; no change within the last three month) and/or CD4 count \>500/ μL, no signs or symptoms of immunosuppression. Pregnant HIV-positive participants must agree to attend all prenatal visits foreseen in the time and events schedule for regular follow-up.
* Note: HBV-positive pregnant women will receive treatment according to the National guidelines and can be enrolled as long as their general condition is good. The decision to enrol falls under the discretion of the PI.
* Note: Participants who test positive for syphilis at screening can be reassessed for enrolment after treatment has been provided.
6. The participant must be pregnant with a singleton pregnancy.
7. The participant must live in the Boende health zone or its surrounding health zones in the Tshuapa province of the DRC.
8. The participant must be willing to deliver her child to the General Referral Hospital of Boende (the trial site location) or the satellite sites Motema Mosantu Health Centre or Marie-Louse Health Centre or the participant must be willing to inform the study staff when labour has started (either through the GRH or satellite site staff, through family or via mobile phone).
9. The participant must agree to follow the study protocol, including attending follow-up visits and reporting delivery plans and any adverse events.
10. The participant must be available and willing to participate and for her unborn child to participate for the duration of the study.
11. The participant must be willing to provide verifiable identification, such as iris scanning or a participant card where feasible, and have means to be contacted (phone number or address).
Inclusion criteria for the Maternal Group 3:
1\. Close contact in the 2 weeks prior to signing the ICF with anyone known to have mpox.
Exclusion Criteria:
1. Known history of cowpox, mpox or vaccinia infection.
2. Close contact in the 2 weeks before signing the ICF with anyone known to have mpox.
\- Note: not applicable to Maternal Group 3
3. Known history of or active autoimmune disease (vitiligo or thyroid disease requiring thyroid replacement are not exclusions), history of Guillain-Barré syndrome or Reye's syndrome.
4. Having received any smallpox or licensed or investigational poxvirus-based (e.g. ACAM2000, MVA-BN based like MVA-BN-Filo) vaccine in the past.
5. Must not have received another experimental or non-licensed vaccine within 4 weeks before receiving the MVA-BN vaccine and during the trial.
6. Known allergy or history of anaphylaxis or other severe adverse reactions to vaccines or vaccine products (including any of the constituents of the study vaccines), including known allergy to egg, egg products and aminoglycosides.
7. History of allergic disease or reactions likely to be exacerbated by any component of the vaccine, e.g., tris(hydroxymethyl)-amino methane, including a history of allergic asthma.
8. Acute or chronic medical condition that, in the opinion of the investigator, would render the trial procedures unsafe or would interfere with the evaluation of responses, including but not limited to neurologic, cardiovascular, respiratory, hepatic, hematologic, rheumatologic, endocrine, gastrointestinal, renal, autoimmune, or immunosuppressive conditions.
\- Note: Participants with minor acute illnesses such as mild diarrhoea or mild upper respiratory tract infection or temperature ≥38.0ºC at screening will be excluded from enrolment at that time but may be rescheduled for re-screening later if feasible.
9. Presence of significant medical conditions or clinically significant findings at screening or vital signs for which, in the opinion of the gynaecologist/medical doctor, participation would not be in the best interest of the participant (e.g., compromise the safety or well-being) or that could prevent, limit, or confound the protocol-specified assessments.
* Note: Participants who have recently received treatment for acute, uncomplicated malaria are eligible for participation if at least 3 days have elapsed from the conclusion of a standard, recommended course of therapy for malaria; participants who are acutely ill with malaria at the time of screening should complete therapy and wait an additional 3 days after completion before screening for the study.
* Note: Participants with sickle cell trait can be included.
10. History of malignancy other than squamous cell or basal cell skin cancer, unless there has been surgical excision at least 6 months prior to screening that is considered to have achieved cure
11. Clinically significant mental disorder not adequately controlled by medical treatment.
12. Active or recent (within 6 months before screening) chronic alcohol abuse and/or intravenous and/or nasal drug abuse.
13. Recent blood donation (including platelets, plasma, and red blood cells) within 4 weeks before screening or planned blood donations during the active trial period.
14. Chronic systemic administration (defined as more than 14 days) of \>5 mg prednisone (or equivalent)/day or any other immune-modifying drugs from 3 months before the first trial vaccination to the visit at the end of the active trial period (use of topical, inhaled, ophthalmic, and nasal glucocorticoids is allowed).
\- Note: Participants receiving antiretroviral (ARV) medication for the management of HIV infection are eligible for inclusion, provided they meet inclusion criterion 5.
15. History of coronary heart disease, myocardial infarction, angina, congestive heart failure, cardiomyopathy, stroke or transient ischemic attack, uncontrolled high blood pressure, significant arrhythmia with or without corrective/ablative surgery, or any other heart condition under the care of a doctor.
16. Major surgery (per the investigator's judgment) within the 4 weeks before screening or planned major surgery during the study (from the start of screening onwards).
17. Post-organ and/or stem cell transplant, whether or not with chronic immunosuppressive therapy.
18. Administration or planned administration of immunoglobulins and/or any blood products from 3 months prior to the first trial vaccination until the visit at the end of the active trial period (packed red blood cells given for an emergency indication in an otherwise healthy person and not required as ongoing treatment is not exclusionary \[e.g., packed red blood cells given in an emergency during elective surgery\])
19. Received an investigational or nonregistered drug or vaccine or used an invasive investigational or nonregistered medical device within 30 days prior to vaccination or current or planned participation in another clinical study during the study.
\- Note: Participation in an observational clinical study is allowed.
20. History of chronic urticaria (recurrent hives).
21. Employment with the investigator or study site, with direct involvement in the proposed study or other studies under the direction of that investigator or study site, or relationship to the investigator or study site employee.
Additional inclusion criteria for Maternal Group 3:
1\. No symptoms at the time of reporting/vaccination.
