Evaluation of Long-term Immunogenicity of a Boost Dose of MVA-BN Vaccine

This study is evaluating how long protection lasts after a booster (third) dose of the MVA-BN vaccine — the vaccine used against mpox (formerly known as monkeypox) — in men who have already completed the two-dose initial series and are eligible for a booster. **You may be eligible if...** - You are a man aged 18 or older - You have already received two doses of the MVA-BN vaccine - You are eligible for and wish to receive a booster dose according to public health recommendations - You are receiving or planning to start HIV pre-exposure prophylaxis (PrEP) - You are covered by French social security **You may NOT be eligible if...** - You have previously had mpox (confirmed by a lab test) - You are under legal guardianship or court protection - You have a medical contraindication to the mpox vaccine Talk to your doctor to see if this trial is right for you.