Yellow fever in Asia-a risk analysis

Area of Science:

• Epidemiology
• Medical Entomology
• Public Health

Background:

• Yellow fever (YF) establishment in Asia is a growing concern due to increased urban outbreaks and global travel.
• The 2016 Angola outbreak introduced YF cases into China, highlighting potential risks despite Asia's historical absence of the disease.
• Quantifying YF outbreak risk in Asia is a public health priority due to potential fatalities and economic impact.

Purpose of the Study:

• To quantify the risk of YF introduction into Asia via international air travel.
• To estimate the potential for autochthonous YF transmission in Asian cities with competent mosquito populations.

Main Methods:

• Utilized international flight data and 2016 YF incidence estimates to model YF introduction risk.
• Employed a temperature-dependent model for YF transmission potential, considering mosquito competence and using a branching process model.

Main Results:

• Estimated 25 Asian cities at risk of receiving at least one viraemic traveler in 2016.
• Calculated a <50% probability of autochthonous YF transmission in all assessed cities at average temperatures, primarily due to low introduction numbers.
• Found limited evidence for travel-related autochthonous YF transmission in 2016.

Conclusions:

• The historic absence of YF in Asia may be linked to a limited number of introductions.
• Increased travel volume or YF incidence could elevate future introduction and transmission risks.
• The developed model aids surveillance by estimating introduction and outbreak risks, especially given asymptomatic infections.