Is the smallpox vaccine effective against mpox?

Yes. Smallpox vaccines provide cross-protection against mpox because both viruses are orthopoxviruses. The JYNNEOS vaccine (MVA-BN, Imvamune/Imvanex) is specifically approved for both mpox and smallpox prevention. ACAM2000 (the replication-competent vaccinia vaccine) is also protective but carries more side-effect risks. Pre-1980 smallpox vaccination campaigns conferred approximately 85% protection against mpox; that immunity has waned in the global population since routine vaccination stopped. JYNNEOS is now recommended as a 2-dose series for at-risk individuals in many countries.