Mpox Vaccines

Multiple vaccines developed for smallpox are currently being made available globally as medical countermeasures for mpox. In the United States, the modified vaccinia Ankara-Bavarian Nordic (MVA-BN, sold as JYNNEOS) and ACAM2000 are the only vaccines approved for the prevention of both smallpox and mpox. For more information on the regulatory status of mpox vaccines in the United States, please consult the Food and Drug Administration.

NIAID has provided significant support in the development of MVA-BN as an alternative to other smallpox vaccines known to can cause severe side effects in people with weakened immune systems and individuals with eczema. NIAID-supported research on MVA-BN includes preclinical evaluation through Phase 2 clinical trials:

• NIAID-funded studies evaluated the vaccine’s safety, immunogenicity, duration of protection and route of administration; the Biomedical Advanced Research and Development Authority (BARDA), part of the U.S. Department of Health and Human Services, supported the advanced clinical evaluation of the vaccine. The U.S. Food and Drug Administration approved JYNNEOS in 2019 for individuals at high risk for smallpox or mpox.
• NIAID supported nonhuman primate studies to determine the effectiveness of vaccination when administered concurrently with the antiviral tecovirimat. Researchers found that that the immune responses induced by the JYNNEOS vaccine or the ACAM2000 smallpox vaccine were not significantly affected by concomitant treatment, and the animals were protected against MPV.
• In 2024, a NIAID-supported study reported that a dose-sparing intradermal mpox vaccination was safe and generated an antibody response equivalent to that induced by the standard regimen at six weeks (two weeks after the second dose). NIAID supported previous research evaluating intradermal administration of MVA-BN, which provided the basis for several regulatory decisions on the vaccine. Because there are no defined correlates of protection against mpox—immune processes confirmed to prevent disease—these findings cannot predict the efficacy of dose-sparing regimens with certainty. Real-world data from the Centers for Disease Control and Prevention and others have shown similar vaccine effectiveness for the dose-sparing regimen given intradermally and the standard regimen given subcutaneously. 
• A study of the standard MVA-BN regimen in adolescents will soon report findings.