Yellow Fever Season in Kenya
In Kenya, yellow fever virus transmission typically increases during the rainy season, with peak transmission occurring in the middle of the rainy season (around August) and reaching its highest levels during the early dry season (October). 1
Transmission Patterns in Kenya and Africa
- Yellow fever is a mosquito-borne viral disease that has caused several documented outbreaks in Kenya, with the first recorded outbreak occurring in 1992-1993, and subsequent outbreaks in 1993,1995,2011, and most recently in 2022 2, 3
- In intermediate zones of West Africa and Kenya, yellow fever virus activity increases during the middle of the rainy season (around August) and peaks during the early dry season (October) 1
- This seasonal pattern corresponds to the period of maximum longevity of mosquito vectors, as increased temperature, humidity, and rainfall lead to higher mosquito abundance and consequently increased viral circulation 1
Vector-Specific Transmission Considerations
- When Aedes aegypti mosquitoes are involved in transmission, yellow fever can occur even during the dry season because these mosquitoes breed in containers used for water storage, making their reproduction less dependent on rainfall 1
- In Kenya, transmission typically follows a sylvatic (jungle) cycle involving forest mosquitoes, but urban outbreaks involving Aedes aegypti can occur year-round 1, 3
Risk Assessment for Travelers to Kenya
- A traveler's risk for acquiring yellow fever is determined by multiple factors including:
Prevention Recommendations
- Yellow fever vaccine is recommended for all travelers aged ≥9 months visiting areas of Kenya where yellow fever is endemic 4, 5
- Vaccination should be administered at least 10 days before travel to ensure immunity 1, 4
- All travelers should take precautions to avoid mosquito bites, including using insect repellents containing DEET, wearing permethrin-impregnated clothing, and staying in accommodations with screened windows or air conditioning 1, 4
Common Pitfalls and Caveats
- A lack of reported human cases in an area does not necessarily indicate absence of risk for transmission 1, 6
- Even during traditionally "low-risk" seasons, yellow fever can still be transmitted, particularly in urban settings with Aedes aegypti mosquitoes 1
- Kenya has experienced sporadic but serious yellow fever outbreaks, with case-fatality rates of approximately 19% in confirmed cases 3, 6
- The risk for acquiring yellow fever is difficult to predict due to variations in ecological determinants of virus transmission 1, 7