During the mpox outbreak, there was limited availability of the modified vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccine which led Canadian health authorities to recommend a single dose for high-risk individuals. Researchers later analysed the effectiveness of this single dose by comparing 3,204 vaccinated and 3,204 unvaccinated people, with a median age of 35 and 22% living with HIV. Results showed that mpox infection occurred less frequently among the vaccinated group, with 21 cases versus 50 in the unvaccinated group, indicating 58% effectiveness for a single dose.

In the United States, tecovirimat—a medication stockpiled for smallpox treatment—was also made available for mpox under a special access protocol due to its effectiveness against similar viruses in animal models. An observational study followed 1,043 mpox patients, where the majority were male, 52% were co-infected with HIV, and 4% were severely immunocompromised. The data revealed that 15% of patients had been vaccinated with MVA-BN. Hospitalisation rates were 4% across all patients but rose to 43% among severely immunocompromised individuals. For most people, lesions healed within 14 days of treatment, though 20 individuals died, 18 of whom were severely immunocompromised.

These findings highlight the effectiveness of even a single vaccine dose in reducing mpox risk, particularly for high-risk populations, and the critical role of targeted antiviral treatments like tecovirimat for severe cases.