1. In this case-control study, adults with mpox were less likely to have been partially or fully vaccinated with the JYNNEOS vaccine compared to those without.
2. The adjusted effectiveness of the JYNNEOS vaccination amongst participants with two doses was estimated to be 66%.
Evidence Rating Level: 2 (Good)
Study Rundown: Mpox is a viral illness that can be transmitted to humans from contact with other infected humans, animals, or contaminated materials. Recently, a large global outbreak of mpox was reported, to which the Food and Drug Administration within the United States responded with approval of an emergency authorization for the use of the JYNNEOS vaccine. Currently, evidence in support of the effectiveness of the JYNNEOS vaccine is largely derived from animal studies and immunogenicity studies. The purpose of this case-control study was to evaluate the effectiveness of the JYNNEOS vaccine (either partial or full vaccination) against mpox within the human population. Primary results of the study found that participants who were confirmed to have mpox were less likely than those without to have been vaccinated with either a partial or full dose of the JYNNEOS vaccine. As this was an observational study by design, the results of the study are primarily limited by causality. As such, prospective longitudinal studies will be helpful in both answering the question of causality for this observed association, as well as clarifying the safety profile of this vaccine amongst humans. Overall, this study contributed positively to the body of evidence that the JYNNEOS vaccine may be beneficial against mpox in adults.
Click to read the study in NEJM
In-Depth [case-control study]: This study utilized a case-control design with data from an integrated electronic health records system to estimate the effectiveness of the JYNNEOS vaccine against mpox disease in adults. The primary outcome of interest was vaccine effectiveness of both partial and full vaccination as compared between case and control groups. Secondary outcomes included additional analysis of vaccine effectiveness by route of administration amongst fully vaccinated adults. Participants with previously confirmed mpox diagnosis or a positive laboratory test were excluded from the control group. Participants without any documented medical encounters in the three years prior to their index event or with a telehealth visit alone were excluded from the study. Subsequently, 2,266 case participants were matched in a 1:4 ratio to 8,649 control participants Primary results of the analysis found that the estimated adjusted effectiveness of JYNNEOS amongst participants with full vaccination was 66.0% (95% Confidence Interval [CI], 47.4 to 78.1), and 35.8% amongst participants with partial vaccination (95% CI, 22.1 to 47.1). The adjusted vaccine effectiveness for a heterogenous route of administration was 75.2% (95% CI, 48.0 to 88.2). This study adds to the literature base in support of the hypothesis that the JYNNEOS vaccine may be beneficial against mpox disease in adults. Large, prospective, randomized studies will be helpful in clarifying the question of causality.
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