As of the end of March, more than 30,000 mpox cases had been reported in the United States in an outbreak that has disproportionately affected gay, bisexual, and other men who have sex with men (MSM), as well as those who are transgender.

With the Jynneos vaccine (Modified Vaccinia Ankara vaccine, Bavarian Nordic) approved by the FDA in 2019 for the prevention of smallpox and mpox via SC injection as a two-dose series (0.5 mL per dose, administered 4 weeks apart), the FDA issued an Emergency Use Authorization to expand vaccine access last August. That allowed a dose-sparing intradermal injection of Jynneos as a two-dose series (0.1 mL per dose, administered 4 weeks apart). Vaccination was made available to those with known or presumed exposure to a person with mpox (postexposure prophylaxis), as well as those at increased risk for mpox or who might benefit from vaccination (preexposure mpox prophylaxis).

Information on vaccine effectiveness has been limited until now. The CDC conducted matched case-control study in 12 U.S. jurisdictions, including nine Emerging Infections Program sites and three Epidemiology and Laboratory Capacity sites. The goal was to evaluate vaccine efficacy (VE) against mpox among MSM and transgender adults aged 18 to 49 years.

During August 19, 2022, to March 31, 2023, 309 case patients were matched to 608 control patients. The results indicated that adjusted VE was 75.2% (95% CI, 61.2%-84.2%) for partial vaccination (one dose) and 85.9% (95% CI, 73.8%-92.4%) for full vaccination (two doses).

In addition, the study found that adjusted VE for full vaccination by SC, intradermal, and heterologous routes of administration was 88.9% (95% CI, 56.0%-97.2%), 80.3% (95% CI, 22.9%-95.0%), and 86.9% (95% CI, 69.1%-94.5%), respectively. Adjusted VE for full vaccination among immunocompromised participants was 70.2% (95% CI, –37.9%-93.6%) and among immunocompetent participants was 87.8% (95% CI, 57.5%-96.5%), according to the research published in the Morbidity & Mortality Weekly Report.

The authors concluded that Jynneos “is effective at reducing the risk for mpox. Because the duration of protection of one versus two doses remains unknown, persons at increased risk for mpox exposure should receive the two-dose series as recommended by the Advisory Committee on Immunization Practices (ACIP), regardless of administration route or immunocompromise status.”

The CDC pointed out that the study is the first to estimate VE by route of administration. “Similar point estimates and overlapping CIs for estimates by route of administration suggest that, in the context of the current outbreak, vaccine administration by any route provides comparable protection against mpox,” the CDC added.

The authors advised that additional research is needed to assess duration of protection, which might differ by number of doses or route of administration. They added that Jynneos vaccination coverage “among persons at risk is low, and many eligible persons have not received both doses. For optimal protection, persons at risk for mpox should receive the two-dose series, as recommended by ACIP, irrespective of administration route.”

The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.

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