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Estimating the size of the monkeypox virus outbreak in Nigeria and implications for global control
Anindita Marwah1, Dimie Ogoina2, Natalie H Au1
1BlueDot, Toronto, Canada.
Background:
A multi-country outbreak caused by monkeypox virus (MPXV) has been unfolding across endemic and non-endemic countries since May 2022. Throughout April and May 2022, Nigeria reported 31 MPXV cases, of which 11 were confirmed via testing. In May 2022, three internationally exported cases of MPXV, presumed to have originated in Nigeria, were reported, suggesting that a larger than reported outbreak might be occurring in the country.
Methods:
We used previously established methods to estimate the true size of the MPXV outbreak in Nigeria. We estimated the incidence rate of exported MPXV cases among all outbound international air travellers from Nigeria during the time period of April and May 2022, using forecasted air traveller volumes. We then applied this incidence rate to the entire population of Nigeria during April and May 2022 assuming that the rate of infection was the same in Nigeria for both travellers and the resident population. Information on the subset of population that were considered to be travellers was obtained from the United Nations World Tourism Organization (UNWTO).
Results:
We estimated that there were approximately 4000 (N = 4013; 95% CI: 828-11 728) active cases of MPXV in Nigeria in April and May 2022. This is approximately 360-fold greater than the confirmed number and approximately 130-fold greater than the reported number of cases in Nigeria.
Conclusion:
Our findings suggest that a larger outbreak than is appreciated may be ongoing in Nigeria. The observed international spread of MPXV offers important insights into the scale of the epidemic at its origin, where clinical detection and disease surveillance may be limited. These findings highlight the need to expand and support clinical, laboratory, and public health capacity to enable earlier detection of epidemics of international significance.
Insights
The monkeypox virus (MPXV) outbreak in Nigeria was significantly larger than reported, with an estimated 4000 cases in April-May 2022. This highlights the need for improved surveillance and public health capacity.
Area of Science:
- Epidemiology
- Public Health
- Virology
Background:
- A multi-country monkeypox virus (MPXV) outbreak began in May 2022.
- Nigeria reported 31 MPXV cases in April-May 2022, with 11 confirmed.
- Three internationally exported cases suggested a larger, unreported outbreak in Nigeria.
Purpose of the Study:
- To estimate the true size of the MPXV outbreak in Nigeria.
- To assess the scale of the epidemic at its origin.
- To inform public health strategies for early detection.
Main Methods:
- Estimated MPXV incidence rate among international air travelers from Nigeria.
- Utilized forecasted air traveler volumes and UNWTO data.
- Applied the incidence rate to the Nigerian population for April-May 2022.
Main Results:
- Estimated approximately 4000 active MPXV cases in Nigeria (95% CI: 828-11,728).
- This represents a 360-fold increase over confirmed cases.
- Indicates a 130-fold increase over reported cases in Nigeria.
Conclusions:
- A substantial MPXV outbreak in Nigeria was likely underestimated.
- International spread provides insights into epidemic scale at the source.
- Enhanced clinical, laboratory, and public health capacity is crucial for early epidemic detection.
