The estimated vaccine effectiveness (VE) of one subcutaneous dose of the Jynneos mpox vaccine among men in Israel was 86%, suggests an observational, real-world study published yesterday in Nature Medicine.
A team led by Clalit Health Services researchers in Tel Aviv examined the electronic health records of 2,054 men eligible for a Jynneos dose on Jul 31, 2022, 1,037 (50%) of whom were vaccinated during the study and completed at least 90 days of follow-up. The age range was 18 to 42 years.
The authors noted that the US Food and Drug Administration (FDA) recommends that Jynneos be given as two doses 4 weeks apart, but amid low vaccine supplies, many countries have been giving mpox patients a single subcutaneous dose (underneath the skin, into the fat layer) followed by a smaller intradermal dose (just underneath the outer, epidermal layer of skin).
However, the efficacy of any dosage of the vaccine, a third-generation smallpox vaccine, against mpox hasn't been proven in human clinical trials. During the now-waning global outbreak, first recognized in May 2022, 85,449 men in 110 countries have been diagnosed as having mpox, and 89 have died. The vast majority of mpox patients in the outbreak have been men who have sex with men.
Few infections overall
During the study, mpox infections were confirmed in five vaccinated participants (9.3 per 100,000 person-days), compared with 16 in the unvaccinated (4.3/100,000) (hazard ratio, 0.14). The estimated, adjusted VE was 86% (95% confidence interval, 59% to 95%).
Completing the second vaccine dose, per the approved label, may improve this effectiveness and provide longer-lasting protection.
"Our results suggest that a single dose of subcutaneous MVA-BN [Jynneos] in this high-risk cohort is associated with a significantly lower risk of MPXV [mpox virus] infection," the authors wrote. "Nevertheless, completing the second vaccine dose, per the approved label, may improve this effectiveness and provide longer-lasting protection."
The authors did not directly control for sexual behaviors among study volunteers, but they factored in data that could serve as a surrogate, such as previous sexually transmitted infections and receipt of HIV drugs. They called for randomized, controlled trials to produce direct evidence of VE.