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Date: August 24, 2024
A recent study published in Eurosurveillance has revealed that childhood smallpox vaccination may provide protection against infections caused by monkeypox virus (MPXV) clade II, particularly among men. This research, conducted by a team from the European Centre for Disease Prevention and Control (ECDC), World Health Organization (WHO), and national public health institutes in Denmark, France, the Netherlands, and Spain, highlights a potentially significant public health implication in light of recent mpox outbreaks.
Study Overview
The study was prompted by the mpox outbreak in Europe during 2022-2023, which predominantly affected men who have sex with men and involved high-risk behavior. Researchers aimed to assess the effectiveness of historical smallpox vaccination in preventing laboratory-confirmed mpox cases. The investigation focused on cases from countries where data on prior smallpox vaccination status and historical vaccination coverage were available.
Countries Included:
- Denmark
- France (mainland only)
- The Netherlands (mainland only)
- Spain
The study analyzed cases of mpox from individuals born during the peak of national smallpox vaccination campaigns, which concluded around 1971. Due to a low number of cases among females, the analysis was limited to male cases.
Key Findings
- Historical Smallpox Vaccination Coverage: Vaccination coverage was high (80-90%) in all included countries until the late 1960s, with a notable decline in the last decade of the vaccination programs.
- Vaccine Effectiveness: The effectiveness of prior smallpox vaccination against mpox caused by MPXV clade II varied significantly:
- Netherlands: 42%
- Spain: 84%
The pooled vaccine effectiveness estimate across all countries was approximately 70%, with a broad 95% confidence interval (23-89%), indicating substantial variability and uncertainty in the results.
Public Health Implications
The study suggests that childhood smallpox vaccination may protect about two-thirds of men against mpox caused by MPXV clade II. However, the varying effectiveness across different countries and the wide confidence intervals highlight the need for further research to validate these findings. The results are not yet sufficient to recommend differential smallpox vaccination strategies based on historical vaccination status or age.
The authors advocate for the provision of mpox vaccination to individuals at high risk of exposure, irrespective of their historical smallpox vaccination status. Given the recent rise in clade Ib mpox cases in central and East Africa, there is an urgent need for additional studies to evaluate the smallpox vaccine’s effectiveness against the latest circulating strains.
For more information: Effectiveness of historical smallpox vaccination against mpox clade II in Denmark, France, the Netherlands and Spain, 2022, Eurosurveillance (2024). DOI: [10.2807/1560-7917.ES.2024.29.34.2400139](https://www.eurosurveillance.org/conte … S.2024.29.34.2400139)
