A study led by Nigeria’s Institute of Human Virology, with collaborators including the University of Cambridge, was published in Nature Communications. The team analysed 176 archived blood samples from healthy adults who had joined SARS-CoV-2 vaccine studies: healthcare workers sampled in 2021 and community volunteers sampled in 2023. Participants had not received mpox or smallpox vaccination in adulthood and were not known contacts of mpox cases.
Laboratory results indicated that 14 per cent of participants retained antibodies associated with historic smallpox vaccination, a pattern concentrated in people born before 1980, the last generation to receive routine childhood smallpox shots. On follow-up—typically after around nine months—about 3 per cent of participants developed a new immune response consistent with recent mpox exposure. Those individuals had no recorded mpox diagnosis and did not report related symptoms.
The researchers also examined more than 100 mpox genomes from across Nigeria; the genetic evidence points to continued but low-level circulation, shaped in part by residual immunity in older people. Ravindra Gupta, a senior author, said the findings indicate sustained low-level transmission rather than unchecked spread. The study highlights a surveillance blind spot because Nigeria’s system depends on people with visible symptoms. Experts such as Alash’le Abimiku and Adam Abdullahi suggested antibody-based testing of blood samples to detect hidden exposure and to better target vaccination. Addressing this gap will require new diagnostic approaches and stronger monitoring beyond symptom-based reporting.
Difficult words
- archive — to store records or materials for later usearchived
- antibody — protein made by immune system to fight infectionsantibodies
- retain — to keep something or continue to haveretained
- circulation — movement or spread of something within a population
- residual — remaining after the main part is gone
- surveillance — careful monitoring to detect problems or disease
- genome — the complete set of genetic material in an organismgenomes
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Discussion questions
- What are the advantages and limits of using archived blood samples for detecting hidden infections in a population?
- How might residual immunity in older people affect decisions about who should be offered mpox vaccination? Give reasons based on the article.
- What practical changes to surveillance and diagnostics could help detect low-level transmission that symptom-based reporting misses?
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