A new Nigerian study has uncovered substantial evidence of previously undetected exposure to mpox among young people presenting with fever at health facilities in four states, raising concerns that the burden of the disease may be higher than routine surveillance figures suggest.
The study, published in Frontiers in Public Health on September 15, 2026, found evidence of antibodies against monkeypox virus (MPXV) among febrile patients in Ondo, Benue, Plateau and Osun states.
Researchers from the Institute of Genomics and Global Health at Redeemer’s University, Ede, and other institutions analysed blood samples from 245 febrile patients aged 15 to 36 years.
Using two different statistical approaches, the researchers estimated that between about one-fifth and nearly one-third of the participants had antibodies indicating exposure to MPXV.
The more rigorous R-based SeroNIST approach estimated seroprevalence at 30.51 per cent for the A35R antigen and 21.17 per cent for the A29L antigen.
Using a conventional three-standard-deviation threshold, the corresponding estimates were higher, at 47.4 per cent and 40.4 per cent, respectively.
The researchers said the differences between the two methods highlighted the importance of using robust statistical approaches when interpreting serological studies.
What the findings mean
Serological testing looks for antibodies produced by the body following exposure to an infection. Unlike PCR, which is primarily useful for detecting an active infection during a limited window, antibody testing can provide evidence of previous or unrecognised exposure.
The researchers said this was particularly important for mpox because its symptoms can overlap with those of other common causes of fever in Nigeria, including malaria, typhoid fever and viral haemorrhagic fevers.
This overlap can make clinical diagnosis difficult, potentially allowing some infections to go undetected.
The study therefore focused on febrile patients attending healthcare facilities, describing them as a potentially important group for surveillance.
The researchers found that 62 of the 245 participants — 25.31 per cent — reacted to both MPXV antigens tested, while others reacted to only one of the two.
The findings, they said, provide evidence of MPXV exposure among people seeking healthcare and suggest that surveillance based only on clinically recognised cases may not capture the full extent of exposure.
Four states, but not the whole country
The study involved patients from 15 healthcare sites across four states: Ondo, Benue, Plateau and Osun.
Ondo contributed the largest number of participants, with 108, followed by Benue with 74, Osun with 32 and Plateau with 31.
The researchers found significant differences in seropositivity according to state of residence, suggesting that geographical factors may influence exposure patterns.
They noted that differences in ecology, human-animal interaction, animal reservoirs and previous outbreak history could contribute to the geographical variation.
However, the authors cautioned against interpreting the findings as representative of the entire Nigerian population.
The study used convenience sampling rather than random population sampling, and all participants were febrile patients attending selected healthcare facilities. The researchers also acknowledged that the study did not collect information on participants’ previous contact with infected people or animals, travel history, vaccination history or previous mpox infection.
Why young people were studied
The researchers deliberately restricted participation to people aged 15 to 36 years.
One reason was to reduce the possibility that antibodies detected in older people might have resulted from smallpox vaccination, which was discontinued in 1980.
The study population consisted mainly of young people, with 147 participants aged 15–25 and 98 aged 26–36.
Women accounted for 156 participants, or 63.7 per cent, while men accounted for 89, or 36.3 per cent.
The researchers cautioned that the greater representation of women could limit the extent to which the findings can be generalised to the wider population.
Implications for mpox surveillance
The researchers said the findings support the integration of serological surveillance into existing mpox monitoring systems in Nigeria.
They recommended combining antibody testing with molecular diagnostics and genomic surveillance to obtain a clearer picture of the virus’s circulation and transmission.
According to the researchers, serological surveillance could help identify previously undetected exposure and monitor changes in population-level exposure, while PCR remains important for confirming active infection.
They also proposed incorporating multiplex serological testing into sentinel surveillance of febrile illnesses.
The study’s authors called for larger, longitudinal and region-specific studies to establish how mpox exposure changes over time and across different parts of Nigeria.
They also stressed that antibody tests cannot completely distinguish MPXV exposure from exposure to other orthopoxviruses, meaning the results should be interpreted cautiously.
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