The JYNNEOS vaccine confers significant protection against monkeypox virus infection among adult men in the United States. Compared with unvaccinated men, the incidence of infection significantly decreases among those who are vaccinated, especially those who receive 2 vaccine doses. These study results were published in Morbidity and Mortality Weekly Report (MMWR).
Researchers evaluated the incidence of monkeypox infection among individuals who received either 1 or 2 doses of the JYNNEOS vaccine and those who were unvaccinated. Data on 9544 incident monkeypox diagnoses occurring among US men (age range, 18-49 years) between July 31 and October 1, 2022, were assessed. Study participants were stratified by vaccination status to estimate the weekly incidence of infection, defined as the number of monkeypox diagnoses divided by either the number of unvaccinated but vaccine-eligible participants within a given week or the number of participants who were vaccinated 2 weeks earlier. Incidence rate ratios (IRRs) were determined via negative binomial regression, with an indicator variable used to control for the given week. Cox proportional hazards regression was used to compare the effects of 1 vs 2 JYNNEOS vaccine doses.
Among 9544 monkeypox diagnoses included in the analysis, 87.2% were among unvaccinated participants and 12.8% were among vaccinated participants. Of the 1006 participants with a known vaccination date who received 1 vaccine dose, infection onset occurred within 14 days of administration among 61% and at day 14 or later among 39%. For the 392 participants who received 2 vaccine doses, infection onset occurred before receipt of the second vaccine dose in 75.3%, within 13 days of administration in 12.5%, and at day 14 or later in 12.2%.
The estimated incidence of monkeypox infection was found to be higher among unvaccinated participants compared with both those who received either 1 (IRR, 7.4; 95% CI, 6.0-91) or 2 (IRR, 9.6; 95% CI, 6.9-13.2) vaccine doses at least 14 days prior to infection onset.
Further analysis among participants who received 1 vaccine dose and developed monkeypox infection within the following 14 days showed 87.1% and 12.9% received the vaccine subcutaneously and intradermally, respectively. No significant differences in the percentage of vaccinated patients who developed monkeypox infection were noted between those who received 1 vaccine dose via subcutaneous or intradermal administration and the overall population.
Limitations of the study include the potential misclassification of incident monkeypox diagnoses and the inability the control for behavioral differences that may have affected exposure risk. The researchers also were unable to control for differences in patient characteristics, such as underlying medical conditions and HIV-associated immunosuppression.
“This report provides additional data suggesting JYNNEOS vaccine provides protection against mpox [monkeypox], irrespective of whether the vaccine is administrated intradermally or subcutaneously,” the researchers noted. “Persons who are eligible for mpox vaccination should receive the complete recommended 2-dose series to optimize strength of protection,” they concluded.
Payne, AB, Ray LC, Cole MM, et al. Reduced risk for mpox after receipt of 1 or 2 doses of JYNNEOS vaccine compared with risk among unvaccinated persons — 43 U.S. jurisdictions, July 31–October 1, 2022. MMWR Morb Mortal Wkly Rep. 2022;71:1560-1564. doi:10.15585/mmwr.mm7149a5