The U.S. Food and Drug Administration (FDA) has approved a freeze-dried formulation of Bavarian Nordic's Jynneos vaccine for the prevention of mpox and smallpox in adults aged 18 and older. This new formulation offers significant advantages over the previously approved liquid-frozen version, including easier storage, transportation, and an extended shelf life.
The approval follows the FDA's review of a supplemental Biologics License Application (sBLA) submitted by Bavarian Nordic in May 2024. The application was primarily supported by clinical data demonstrating comparable immune responses and safety profiles between the freeze-dried and frozen liquid formulations.
"Today's FDA approval represents a significant milestone in our development of this next generation of Jynneos and in our collaborative efforts with the U.S. government to strengthen public health security," said Paul Chaplin, PhD, President and CEO of Bavarian Nordic.
Clinical Evidence Supporting Approval
The FDA's decision was based on a Phase II clinical trial involving 651 healthy volunteers who received either the liquid-frozen vaccine or the freeze-dried counterpart. Results showed no statistical differences in immune responses between the two groups, and no serious adverse events were recorded. The freeze-dried group did experience slightly higher local reactions at the injection site, but these were not considered clinically significant.
In addition to clinical data, Bavarian Nordic provided comprehensive nonclinical and manufacturing information to support the application.
Advantages for Public Health Preparedness
The freeze-dried formulation addresses key limitations of the original Jynneos vaccine, which requires specific cold-chain storage and transportation. These requirements have posed challenges for stockpiling and distribution, particularly during outbreak situations.
"This approval will provide additional flexibility for stockpiling against a smallpox event or mpox outbreak," Bavarian Nordic stated in a news release.
The improved formulation is particularly significant given the ongoing global mpox situation. The World Health Organization (WHO) continues to classify the mpox outbreak as a public health emergency, with more than 100,000 cases of Clade II mpox reported globally. The United States has recently identified four cases of the more severe Clade I mpox, with the most recent cases detected in New Hampshire and New York in February 2025.
Government Partnership and Stockpiling Efforts
Jynneos was the first smallpox vaccine developed under Project BioShield, a program created by Congress in 2004 to accelerate the development and availability of medical countermeasures against biological threats through public-private partnerships.
The U.S. government has been working closely with Bavarian Nordic to ensure adequate vaccine stockpiles are available in case of future outbreaks. The country has been stockpiling the vaccine since 2010 and intensified these efforts following the 2022-2023 mpox outbreak that affected all 50 states.
In 2017, the Biomedical Advanced Research and Development Authority (BARDA) awarded Bavarian Nordic a contract to develop a freeze-dried version of the vaccine with a longer shelf life to replace existing stockpiles. This was followed by a $156.8 million contract in 2024 to support ongoing efforts.
Manufacturing and Availability
Bavarian Nordic has already initiated manufacturing of the freeze-dried vaccine, with the first deliveries expected later in 2025. The company has also been instrumental in addressing the ongoing mpox outbreak in Africa, having sent more than one million doses of the vaccine to affected countries and committed to further increasing production.
For a time, Jynneos was the only FDA-approved vaccine for mpox prevention. In August 2024, Emergent BioSolutions' ACAM2000 became the second vaccine approved for preventing mpox in high-risk individuals.
The approval of this more stable formulation represents a significant advancement in public health preparedness, particularly as global health authorities continue to monitor and respond to mpox outbreaks worldwide.
