In 1970, the first human case of mpox was reported in the Democratic Republic of the Congo (DRC) in a boy aged 9 months who was the only member of his family without a smallpox vaccination. Receiving a previous vaccination against smallpox was estimated to be 85% effective in preventing monkeypox, although the long-term efficacy of smallpox vaccination was unclear.

Following the first mpox reported in the DRC, mpox subsequently spread to other central and western African countries. Mpox is a zoonotic infection caused by the mpox virus, an orthopoxvirus closely related to the variola virus that causes smallpox