The monkeypox virus is an orthopoxvirus that causes mpox (monkeypox), a disease with symptoms similar to smallpox, although less severe. While smalpox was eradicated in 1980, mpox continued to occur in countries of central and west Africa. Since May 2022, cases have been reported from countries without previously documented mpox transmission outside the African region. Two distinct clades of the monkeypox virus have been identified: Clade I ( previously know as the Congo Basin (central African) clade) and Clade II (the former west African clade). The disease can spread from humans to humans; transmitted through contact with body fluids, lesions on the skin or on internal mucosal surfaces, such as in the mouth or throat, respiratory droplets and contaminated objects.

Vaccines are an important component for an integrated approach to controlling mpox outbreaks. Therefore, on 7 August the WHO Director General opened the Emergency Use Listing procedure for vaccines to prevent against mpox.