A health data simulation has concluded that a single dose of the Modified vaccinia Ankara-Bavarian Nordic (MVA-BN) was 58% effective in protecting again mpox infection, a disease caused by infection with the Monkeypox virus, which is most likely in men who have sex with men and which causes a rash, along with other symptoms. 

After an mpox outbreak in 2022, Ontario, Canada introduced the vaccine as a protective measure for individuals at high risk of exposure. To reach as many as possible, a single dose was used. That seems to have been enough. An analysis of adult men with a history of being tested for syphilis and a bacterial sexually transmitted infection in the previous year, or who filled a prescription for drugs taken to prevent getting HIV, who were vaccinated against mpox were matched to unvaccinated men based on age, area of residence, past HIV diagnosis, number of STI diagnoses, and the receipt of any non-MVA-BN vaccine.


Confirmed mpox infections and number of MVA-BN vaccine doses administered by week in Ontario, Canada, 1 May to 25 December 2022. MVA-BN= modified vaccinia Ankara-Bavarian Nordic

The observational study of infection rates in 3,204 men who received the MVA-BN vaccine and 3,204 unvaccinated men estimates that vaccine effectiveness for a single dose of MVA-BN against mpox infection was 58%. 

The World Health Organisation recently declared a second public health emergency over mpox due to rapid spread across countries in Africa. In the Democratic Republic of Congo alone there have been 18,000 cases of mpox and at least 600 deaths.