JYNNEOS Smallpox Vaccine in Adult Healthcare Personnel at Risk for Mpox in the Democratic Republic of the Congo

Orthopoxvirus infections produce antibody responses that are cross-protective against other viruses within the genus. It is this property of orthopoxviruses that allows a vaccine for vaccinia virus against smallpox to be used to provide protection against mpox. Studies performed during and in the immediate aftermath of smallpox eradication demonstrated that smallpox vaccination (with a first generation vaccine) could confer protection against infection with monkeypox virus. Newer, third generation vaccines such as JYNNEOS, an attenuated (replication deficient) strain of vaccinia virus may offer an alternative safer source of vaccine-derived protection.

The clinical presentation of mpox infection is similar to smallpox, although it is less transmissible human-to-human than smallpox and less deadly (case fatality estimates for mpox are approximately 10%). Naturally-occurring human mpox is largely restricted to remote regions of the Congo Basin forest in Central Africa. This study is the first rigorous evaluation of JYNNEOS in a region where natural Orthopoxvirus transmission occurs at appreciable and predictable rates. Healthcare and frontline workers in the DRC are currently at high risk of acquiring monkeypox virus infection that prevents them from performing work duties, compromises healthcare delivery in an already fragile system, and can result in death.

This open-label prospective cohort study in up to 1,600 healthcare personnel at risk of mpox infection through their daily work will document monkeypox virus exposure and infection in vaccinated participants while concurrently evaluating the immunogenicity and safety of JYNNEOS vaccine. Study participation is voluntary and open to male and female healthcare personnel ages 18 years and older in Tshuapa Province in the DRC. Participants will receive two subcutaneous doses of JYNNEOS vaccine on days 0 and 28. A subset of study participants will receive a booster dose. Blood samples will be obtained on days 0, 14, 28, 42, 180, 365, 545, and 730 following primary vaccination for immunogenicity analysis. For individuals who receive a booster dose, blood samples will be obtained on Days 3, 7, 14, and \> 1 year following booster vaccination. After each vaccination participants will be observed for at least thirty minutes. They will maintain an adverse event diary to record systemic and local adverse events for 7 days after each immunization. They will also record exposure to the monkeypox virus in an exposure diary that is reviewed at each follow-up visit.

The study will evaluate the proportion of participants who after being vaccinated 1) develop suspected or confirmed mpox infection, and 2) experience exposure to monkeypox virus. The study will also evaluate the safety and immunogenicity of JYNNEOS.