There has been increasing alarm regarding the appearance of yellow fever in the state of Minas Gerais in Brazil where over 100 people have been infected and over 30 killed. A state of emergency has been declared. It may seem, in today's context, yellow fever -- a major historical killer that, to this day, underlies, much government policy on infectious diseases -- shouldn't raise concerns given the availability of an efficacious vaccine, however there is more to the story.
Yellow fever, famously discovered to be transmitted via Aedes mosquito by Walter Reed and his team in Cuba, is a disease that has a spectrum of symptoms ranging from none to jaundice, death, and hemorrhage. Yellow fever has two cycles of infection: a sylvatic one and an urban one. In the sylvatic cycle the virus is passed between non-human primates and humans who come into contact with the mosquitoes in rural areas. In the more dangerous urban cycle, urban mosquitoes become seeded and transmission between humans accelerates.
Vaccination against yellow fever is not universal and is often reserved for travelers to regions at high risk. It is unclear how high the vaccination rates are in Minas Gerais but over 700,000 doses of vaccine have been deployed.
In the days to come, vaccination campaigns and other activities (facilitated by the emergency declaration) will be ramped up and hopefully be able to staunch this outbreak before it becomes widespread as occurred in Angola last year where cases spread to various nations including China.