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. 2025 Jan 20;15(1):2.
doi: 10.1007/s44197-025-00341-w.

Epidemiology of Yellow Fever in Nigeria: Analysis of Climatic, Ecological, Socio-Demographic, and Clinical Factors Associated with Viral Positivity Among Suspected Cases Using National Surveillance Data, 2017-2023

Stephen Eghelakpo Akar  1   2   3 , William Nwachukwu  3 , Oludare Sunbo Adewuyi  1 , Anthony Agbakizua Ahumibe  1   2 , Iniobong Akanimo  3 , Oyeladun Okunromade  3 , Olajumoke Babatunde  3 , Chikwe Ihekweazu  4 , Mami Hitachi  2 , Kentaro Kato  2 , Yuki Takamatsu  5 , Kenji Hirayama  6 , Satoshi Kaneko  7
Affiliations

Epidemiology of Yellow Fever in Nigeria: Analysis of Climatic, Ecological, Socio-Demographic, and Clinical Factors Associated with Viral Positivity Among Suspected Cases Using National Surveillance Data, 2017-2023

Stephen Eghelakpo Akar et al. J Epidemiol Glob Health. .

Abstract

Background: Since its resurgence in 2017, Yellow fever (YF) outbreaks have continued to occur in Nigeria despite routine immunization and the implementation of several reactive mass vaccinations. Nigeria, Africa's most populous endemic country, is considered a high-priority country for implementing the End Yellow fever Epidemics strategy.

Methods: This retrospective analysis described the epidemiological profile, trends, and factors associated with Yellow fever viral positivity in Nigeria. We conducted a multivariable binary logistic regression analysis to identify factors associated with YF viral positivity.

Results: Of 16,777 suspected cases, 8532(50.9%) had laboratory confirmation with an overall positivity rate of 6.9%(585). Predictors of YFV positivity were the Jos Plateau, Derived/Guinea Savanah, and the Freshwater/Lowland rainforest compared to the Sahel/Sudan Savannah; dry season compared to rainy season; the hot dry or humid compared to the temperate, dry cool/humid climatic zone; 2019, 2020, 2021, 2022, and 2023 epidemic years compared to compared to 2017; first, third, and fourth quarters compared to the second; male sex compared to female; age group > = 15 years compared to < 15 years; working in outdoor compared to indoor settings; having traveled within the last two weeks; being of unknown vaccination status compared to being vaccinated; and vomiting.

Conclusion: Ecological, climatic, and socio-demographic characteristics are drivers of YF outbreaks in Nigeria, and public health interventions need to target these factors to halt local epidemics and reduce the risk of international spread. Inadequate vaccination coverage alone may not account for the recurrent outbreaks of YF in Nigeria.

Keywords: Epidemiological profile; Factors associated; Vaccination; Yellow fever.

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Conflict of interest statement

Declarations. Ethical Approval: This study was conducted in accordance with the Declaration of Helsinki. Approval for the study was sought by first submitting our study proposal to the Research Governance Unit of the Nigeria Centre for Disease Control and Prevention (approval number: NCDC/HQ/GCOR/V.III/35; date of approval: April 12, 2021). We sought additional ethical approval from the National Health Research Ethics Committee (approval number: NHREC/01/01/2007-04/10/2023; date of approval: October 4, 2023. Consent to Participate: Patient consent was waived as this study utilized secondary data which has been previously collected, stored, and analyzed as part of outbreak response activity by the NCDC, during which a case investigation form was administered by clinical staff to obtain relevant information from suspected cases of YF to which they consented in writing or orally. In the case of minors, informed consent was given by either a parent or guardian, either in writing or verbal form, depending on their literacy status. The data was confidentially stored in passworded computer systems by the NCDC data management team and was shared in de-identified and anonymized Microsoft Excel format for this study. Competing Interests: The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Time trends of incidence of YF cases in Nigeria, 2017–2023. Lines indicate weekly mean incidence. In: (a) average weekly incidence were stratified by laboratory test result, and (b) average weekly incidence disaggregated by vaccination status. The light green histogram background is the epidemic curve of all suspected cases
Fig. 2
Fig. 2
Age-sex pyramid of Yellow fever cases in Nigeria, 2017–2023. From left to right: (a) all reported cases, (b) vaccinated cases, (c) unvaccinated cases, and (d) cases of unknown vaccination status. The percentage of cases were superimposed on the country’s age-sex population structure. Pink = female and blue = male. The light-shaded bars indicate the country’s demographic age-sex structure
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