MPOX exposure may be occurring silently among healthy adults in Nigeria, according to new research that combines antibody testing with viral genomic analysis. Mpox, formerly known as monkeypox, is a viral infection related to smallpox that can cause fever, rash, and swollen lymph nodes, but infections may also be mild or go unnoticed.
The study examined whether people without symptoms may still be exposed to the mpox virus (MPXV), particularly in populations shaped by historic smallpox vaccination programmes.
Evidence of Hidden Mpox Exposure
Researchers analysed blood samples from 176 Nigerian adults, including healthcare workers and community volunteers, using a multi-antigen antibody test designed to detect immune responses to MPXV. Overall, 13.6% showed evidence of prior mpox exposure at baseline, with most of these individuals born before 1980, the era when routine smallpox vaccination was still in place.
Antibody responses were stronger and broader in this older group, suggesting that residual immunity from smallpox vaccination continues to influence how the immune system recognises mpox decades later.
Asymptomatic Mpox Exposure Over Time
Among 153 participants followed for a median of 9 months, five people (around 3%) developed clear immune signatures of new mpox exposure without reporting any illness. These changes included at least a doubling of antibody responses across multiple viral proteins, a pattern clinicians would typically associate with recent infection.
Notably, the strongest immune responses were seen against specific viral antigens, particularly B6R, although responses varied substantially between individuals. This variability may help explain why mpox exposure does not always lead to recognisable disease.
Genomic Clues to Transmission Patterns
To place these findings in context, the team also analysed more than 100 Nigerian MPXV genomes. The genetic data suggested that while person-to-person transmission does occur, many infections appear to be “dead ends” that do not spread further. This pattern aligns with the observed low-level, often asymptomatic mpox exposure seen in the blood samples.
Implications for Surveillance and Prevention
Together, the findings suggest that mpox exposure may be under-detected by symptom-based surveillance alone. For clinicians and public health teams, this raises important questions about how widely the virus circulates and who may be at risk.
The authors caution that antibody evidence does not prove ongoing infection or infectiousness. However, understanding asymptomatic mpox exposure could help refine surveillance systems and support more targeted vaccination strategies, particularly as global immunity from smallpox vaccination continues to wane.
Reference
Abdullahi A et al. Sero-genomic evidence for occult mpox exposure in healthy Nigerian adults. Nat Commun. 2026;17(1):482.
