Estimates: Jynneos mpox vaccine 84% and 35% effective in people without, with HIV
March 19, 2025
A recent study published in The Lancet Infectious Diseases found that a single dose of the Jynneos vaccine is 58% effective against mpox overall but significantly less effective (35%) in people with HIV compared to 84% in those without. Conducted across multiple countries, the study also highlighted reduced symptom severity and faster recovery in vaccinated individuals. Researchers stress the importance of completing a two-dose regimen, particularly for immunocompromised individuals. Experts call for expanded research in Central Africa, where clade 1 mpox is endemic, emphasizing the need for stronger vaccination strategies to protect high-risk populations and prevent global outbreaks.
A new Lancet Infectious Diseases study has reaffirmed the effectiveness of the Jynneos vaccine in preventing mpox infections, with a single dose providing 58% protection overall. However, the study found striking disparities in vaccine effectiveness (VE), with protection reaching 84% among HIV-negative individuals but dropping to just 35% for those with HIV. Researchers attribute the weaker response to compromised T-cell functionality in people living with HIV, which affects immune protection after vaccination.
Conducted across multiple countries, including Germany, Argentina, and Brazil, the study tracked thousands of men who have sex with men (MSM) and transgender individuals, evaluating both safety and efficacy. Among vaccinated participants, skin lesions healed in a median of 10 days compared to 18 days for the unvaccinated. Systemic symptoms were also reduced, occurring in 45.5% of vaccinated individuals versus 78.2% of unvaccinated participants. No vaccinated individuals required hospitalization, whereas 3% of unvaccinated participants were hospitalized due to severe symptoms.
While no mpox cases occurred among individuals who received both vaccine doses, preventing researchers from assessing two-dose VE, experts emphasize the need for complete vaccination. In an accompanying commentary, public health specialists argue that individuals with compromised immune systems, particularly those with HIV, may require additional booster doses.
Furthermore, experts highlight a critical research gap in Central Africa, where clade 1 mpox remains endemic, yet vaccine access remains limited. Given the virus’s continued spread, particularly among high-risk groups, refining global vaccination strategies with more comprehensive data is a public health imperative. As new mpox outbreaks emerge, ensuring equitable vaccine distribution and conducting further studies on booster requirements will be essential to mitigating future epidemics, particularly in resource-limited regions where the disease burden remains highest.