Mosquitoes can’t fly very far or very fast. Most mosquitoes can fly no more than about one to three miles, and often stay within several hundred feet of where they were hatched. However, a few salt marsh species can travel up to 40 miles. The top speed for a mosquito is about 1.5 miles per hour.
https://www.megacatch.com/mosquito-faqs/mosquito-facts/
Thank you. It sounds as if the author did not need to worry about yellow fever transmission in his particular situation, then.