A new study published in Nature Communications suggests that exposure to mpox can occur without obvious illness, and that immunity from historic smallpox vaccination continues to shape how the virus moves through communities.
Researchers from the University of Cambridge, working with Nigerian partners, analyzed blood samples from healthy adults and found evidence that the virus may circulate unnoticed—posing a challenge to current surveillance systems that rely heavily on symptomatic case detection.
Key Findings
- Silent Exposure Identified: Blood samples from 176 healthy Nigerian adults showed that some individuals had immune markers consistent with recent mpox exposure, despite having no recorded diagnosis or symptoms.
- Historic Smallpox Immunity Still Present: About 14% of participants displayed antibody patterns indicating residual immunity from childhood smallpox vaccination—mainly those born before 1980.
- New Exposure Detected in 2023 Samples: Among 153 participants with follow-up samples collected nine months later, five individuals (around 3%) showed immune changes consistent with recent mpox exposure.
- No Symptoms Reported: None of the newly exposed participants reported symptoms or were clinically diagnosed, suggesting infections may be mild or atypical.
- Transmission Appears Widespread, Not Occupational: No major differences were found between healthcare workers and community volunteers, indicating broader community exposure rather than limited occupational risk.
What This Means for Public Health
Lead author Dr. Adam Abdullahi of the University of Cambridge emphasized that mpox infection may not always follow the “textbook” presentation. He noted that in populations with partial immunity, the virus could spread quietly while leaving detectable immune traces that go unnoticed by standard clinical surveillance.
The study also included genomic analysis of over 100 mpox virus samples collected in Nigeria. Results suggested slow epidemic growth, limited transmission chains, and frequent dead-end spread, consistent with ongoing transmission but constrained by existing immunity.
Calls for Expanded Surveillance
Professor Alash’le Abimiku, Executive Director of the Institute of Human Virology Nigeria, urged broader surveillance methods, saying:
“Instead of relying solely on reported cases or symptoms, monitoring populations by testing blood samples for antibodies will be important for understanding how the virus is spread and guiding targeted vaccination.”
Researchers stressed that the findings do not indicate a large-scale hidden epidemic. Rather, they highlight how mpox may circulate in subtle ways, especially in communities with mixed levels of immunity.