Yellow fever seems to play a role in single, sudden breakouts of the disease. Three epidemiologically different infectious cycles occur, in which the virus is transmitted from mosquitoes to humans or other primates. In the "urban cycle", only the yellow fever mosquito "A. aegypti" is involved. It is well adapted to urban areas, and can also transmit other diseases, including Zika fever, dengue fever, and chikungunya. The urban cycle is responsible for the major outbreaks of yellow fever that occur in Africa. Except for an outbreak in Bolivia in 1999, this urban cycle no longer exists in South America. Besides the urban
Yellow fever vaccine Yellow fever vaccine Yellow fever vaccine is a vaccine that protects against yellow fever. Yellow fever is a viral infection that occurs in Africa and South America. Most people begin to develop immunity within ten days and 99% are protected within one month of vaccination, and this appears to be lifelong. The vaccine can be used to control outbreaks of disease. It is given either by injection into a muscle or just under the skin. The World Health Organization (WHO) recommends routine immunization in all countries where the disease is common. This should typically occur between nine and twelve months