Reduced Odds of Mpox-Associated Hospitalization Among Persons Who Received JYNNEOS Vaccine

California, May 2022-May 2023

Samuel Schildhauer, MPH; Kayla Saadeh, MPH; Josh Vance, MPH, MEd; Joshua Quint, PhD; Tarek Salih, MD; Timothy Lo, MPH; Awa Keinde, MPH; Edwin Chojolan, MPH; Esther Gotlieb, MPH; Marisa Ramos, PhD; Eric Chapman; Philip Peters, MD; Jessica Watson, MD; Kelly A. Johnson, MD; Eric C. Tang, MD; Kathleen Jacobson, MD; Robert Snyder, PhD


Morbidity and Mortality Weekly Report. 2023;72(36):992-996. 

In This Article

Abstract and Introduction


The effectiveness of 1 dose of JYNNEOS vaccine (modified vaccinia Ankara vaccine, Bavarian Nordic) against hospitalization for mpox (caused by Monkeypox virus), has been demonstrated; however, the impact of 2 doses on hospitalization risk, especially among persons infected with HIV, who are at higher risk for severe disease, is an important factor in evaluating vaccine effectiveness against mpox disease severity and Monkeypox virus infection. Surveillance data collected by the California Department of Public Health were used to evaluate whether receipt of 2 doses of JYNNEOS vaccine reduced the odds of hospitalization among persons with mpox. The odds of hospitalization among persons with mpox who had received 1 or 2 JYNNEOS doses were 0.27 (95% CI = 0.08–0.65) and 0.20 (95% CI = 0.01–0.90), respectively, compared with unvaccinated mpox patients. In mpox patients with HIV infection, the odds of hospitalization among those who had received 1 JYNNEOS vaccine dose was 0.28 (95% CI = 0.05–0.91) times that of those who were unvaccinated. No mpox-associated hospitalizations were identified among persons infected with HIV who had received 2 JYNNEOS vaccine doses. To optimize durable immunity, all eligible persons at risk for mpox, especially those infected with HIV, should complete the 2-dose JYNNEOS series.


During May 12, 2022–May 18, 2023, a total of 5,765 persons with mpox and 250 (4.3%) mpox-associated hospitalizations were reported among California residents.[1] At the end of May 2022, California began to distribute JYNNEOS smallpox and mpox vaccine, licensed in the United States as a 2-dose series, with doses administered 28 days apart, for protection against mpox.[2–4] Observational studies of JYNNEOS vaccine effectiveness against mpox have ranged from 66% to 89% for 2 doses and 36% to 75% for 1 dose.[5–7] A 2022 study in 29 jurisdictions found that persons with mpox who had received 1 JYNNEOS dose were less likely to be hospitalized and reported fewer lesions compared with unvaccinated persons with mpox.[8] The effect of 2 JYNNEOS doses on hospitalization risk, especially among persons with HIV infection, who are at higher risk for severe mpox disease, has not been evaluated.[1] This study analyzed reported California mpox cases and immunization registry data to determine the risk for mpox-associated hospitalization by JYNNEOS vaccination status.