T-Cell Receptor Signaling & Squamous-Cell Carcinoma Clearance
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mpox Vaccine Effectiveness Wanes Over Time, But remains protective
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The JYNNEOS vaccine, the primary tool used to combat the 2022-2023 mpox outbreak, provides notable initial protection against infection. Though, new research reveals that its effectiveness diminishes over time, though it continues to offer significant protection against severe illness, hospitalization, and death. This analysis, published on October 9, 2025, in the New England Journal of Medicine, underscores the importance of ongoing monitoring and potential booster strategies.
The Study: Tracking Vaccine Performance
Researchers analyzed data from over 2,000 men who have sex with men (MSM) in the United States. This group was specifically chosen due to their disproportionately high risk of mpox infection during the outbreak. Participants were followed for up to 14 months after receiving their first dose of the JYNNEOS vaccine. The study meticulously tracked new mpox infections, accounting for factors like time since vaccination and individual risk behaviors.
the study design involved prospective cohort analysis, meaning participants were enrolled *before* knowing their mpox status, minimizing bias. Researchers used statistical modeling to adjust for potential confounding variables, such as the number of sexual partners and engagement in high-risk activities.
Key Findings: waning Immunity and Continued Protection
The data revealed a clear trend: vaccine effectiveness declined steadily over time. Initially, the JYNNEOS vaccine demonstrated approximately 85% effectiveness in preventing mpox infection. However, this protection dropped to around 65% after 6-9 months, and further decreased to approximately 50% after 12-14 months.
Importantly, even with waning protection against infection, the vaccine continued to provide strong protection against severe outcomes. Hospitalization rates were significantly lower among vaccinated individuals, even those with reduced vaccine effectiveness against infection. No deaths were reported among vaccinated participants in the study cohort.
| Time Since Vaccination | Estimated Vaccine Effectiveness (Against Infection) |
|---|---|
| 0-3 Months | 85% |
| 3-6 Months | 75% |
| 6-9 Months | 65% |
| 9-12 Months | 55% |
| 12-14 Months | 50% |
Why Does Vaccine Effectiveness Wane?
Several factors likely contribute to the observed decline in vaccine effectiveness. The JYNNEOS vaccine is a modified vaccinia Ankara (MVA) vaccine, which generally elicits a robust but potentially less durable immune response compared to live-attenuated vaccines. The immune response to MVA vaccines tends to rely more on antibody production, which can decline over time.
Furthermore, the emergence of viral variants could play a role. While the study did not specifically analyze the impact of different mpox strains, viral evolution is a constant process, and new variants may exhibit reduced susceptibility to existing vaccines