Yellow fever in Asia. Since the 1980s, the number of cases of yellow fever has been increasing. This is believed to be due to fewer people being immune, more people living in cities, people moving frequently, and changing climate increasing the habitat for mosquitoes. The disease originated in Africa, from where it spread to South America through the slave trade in the 17th century. Since the 17th century, several major outbreaks of the disease have occurred in the Americas, Africa, and Europe. In the 18th and 19th centuries, yellow fever was seen as one of the most dangerous infectious diseases. In 1927
Yellow fever culture the virus and won a Nobel Prize in 1951 for this achievement. A French team developed the French neurotropic vaccine (FNV), which was extracted from mouse brain tissue. Since this vaccine was associated with a higher incidence of encephalitis, FNV was not recommended after 1961. Vaccine 17D is still in use, and more than 400 million doses have been distributed. Little research has been done to develop new vaccines. Some researchers worry that the 60-year-old technology for vaccine production may be too slow to stop a major new yellow-fever epidemic. Newer vaccines, based on vero cells, are in development