Top 5 Takeaways:

  1. Nearly 1 million JYNNEOS doses administered: From May 22 to October 21, 2022, around 987,294 doses were given in the U.S., showing a safety profile consistent with prelicensure studies.
  2. Most common adverse events were nonserious: These included injection site reactions. Serious adverse events were rare in adults, and none identified in persons aged <18 years.
  3. VAERS and VSD systems for monitoring: The Vaccine Adverse Event Reporting System (VAERS) and Vaccine Safety Datalink (VSD) were used for safety surveillance.
  4. Myocarditis and anaphylaxis rates: The VAERS reporting rate for myocarditis is lower than the background rate, and anaphylaxis rates are similar to other vaccines.
  5. Continued safety surveillance: CDC and FDA will persist in monitoring JYNNEOS vaccine safety, and health care providers are encouraged to report adverse events.

Original Article Author and Citation

Corresponding Author

Jonathan Duffy,

Suggested Citation

Duffy J, Marquez P, Moro P, et al. Safety Monitoring of JYNNEOS Vaccine During the 2022 Mpox Outbreak — United States, May 22–October 21, 2022. MMWR Morb Mortal Wkly Rep 2022;71:1555–1559.


The CDC report assesses the safety of the JYNNEOS vaccine used during the 2022 mpox outbreak. About 1 million doses were administered, with the safety profile aligning with pre-licensure studies. The majority of reported adverse events were nonserious, such as injection site reactions. Serious adverse events in adults were rare, and none were reported in individuals under 18 years.


The CDC utilized VAERS, a national surveillance system, and the VSD for safety monitoring. VAERS gathers reports from various sources, while VSD employs electronic health record data for active vaccine safety surveillance. Analysis of adverse event reporting rates was performed, comparing intradermal and subcutaneous administration methods.


The report discusses the significance of these findings in the context of public health practice. It notes the similar rates of anaphylaxis to other vaccines and the lower myocarditis rates compared to live, replicating smallpox vaccines. The most common vaccination “error” was the absence of a wheal in intradermal administration, though it should be noted that such occurrences are still seen as valid administrations of the vaccine.


The study concludes that the JYNNEOS vaccine’s safety profile post-licensure and post-authorization aligns with clinical trial observations. There have been no new or unexpected safety concerns. The report reinforces the importance of continued monitoring and reporting of adverse events related to the JYNNEOS vaccine.


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