The 1970 yellow fever epidemic in Okwoga District Benue Plateau State, Nigeria. 2. Immunity survey to determine geographic limits and origins of the epidemic

Area of Science:

• Epidemiology
• Virology
• Public Health

Background:

• The 1970 yellow fever epidemic in Okwoga District, Nigeria, prompted investigations into its geographic extent.
• Understanding epidemic dynamics is crucial for disease control and prevention strategies.

Purpose of the Study:

• To define the geographic boundaries of the 1970 yellow fever epidemic in Okwoga District.
• To identify any other unrecognized yellow fever foci in surrounding regions.

Main Methods:

• Serological surveys were conducted to detect yellow fever antibodies in human populations.
• Analysis of immune sera distribution to map epidemic zones.

Main Results:

• The 1970 epidemic was geographically limited to Okwoga District, with no evidence of spread to adjacent Benue Plateau and East Central States.
• A distinct, previously unrecognized focus of recent yellow fever epidemic activity was identified in Mbawsi, southern East Central State.
• Elevated levels of yellow fever immunity were observed in Guinea savannah zones within the Benue River basin, outside the identified Okwoga and Mbawsi epidemic areas.

Conclusions:

• The 1970 yellow fever epidemic in Nigeria had a localized geographic distribution.
• The discovery of the Mbawsi focus indicates potential for unrecognized yellow fever outbreaks.
• The Benue River basin's Guinea savannah zones may represent areas of enzootic or epidemic yellow fever activity requiring further surveillance.