Asymptomatic transmission plays a prominent role in mpox infection patterns

To resolve the mystery, researchers from Kaiser Permanente in collaboration with UC Berkeley School of Public Health, tested for the mpox virus using rectal swabs taken to check for other sexually transmitted diseases from men who have sex with men in Southern California during the summer and early fall of 2024. At the same time, the researchers watched electronic health records to see new mpox diagnoses among men enrolled in Kaiser Permanente Southern California health plans.

"From the genomic data, we can reconstruct patterns of transmission looking backward in time," explained Dr. Tartof. "These patterns were inconsistent with a scenario in which the 3% of infections who received diagnoses cause all onward spread."

The study also showed that the mpox vaccine reduced the risk of being diagnosed with mpox by 78 percent and reduced the risk of infection by 50 percent. The study authors said that a renewed focus on mpox vaccination could play a significant role in controlling the outbreak.

"There was a big push to vaccinate people who could be at risk when the outbreak started in 2022," Dr. Lewnard said. "However, vaccination rates have since decreased, and certain populations may not have been reached during the initial campaign, such as people who were in long-term relationships or who were younger and not sexually active in 2022."

He added: "Unvaccinated people face risk of severe disease if they are exposed to mpox, and our findings suggest this risk is greater than we previously understood."

Source:Journal reference:

Lewnard, J. A., et al (2026) Extensive cryptic circulation sustains mpox among men who have sex with men. Nature Communications. DOI:10.1038/s41467-026-72749-2. https://www.nature.com/articles/s41467-026-72749-2.