Researchers pinpoint potential spread of yellow fever

Scientists have determined the yellow fever virus has the potential to spread into cities around the world where it previously hasn’t been seen.

The study findings of St. Michael’s Hospital in Toronto published in the Bulletin of the World Health Organization detailed the mapping of yellow fever virus spread by analyzing global patterns of airline travellers, environmental conditions needed to enable transmission of the virus within a city, and countries’ requirements for travellers to provide proof of yellow fever vaccination upon entry.

“Imagine a yellow fever outbreak as a fire,” Dr. Kamran Khan, a scientist at the Li Ka Shing Knowledge Institute of St. Michael’s Hospital, said. “Embers can fly off in different directions, and if they land in the right place, they can create another fire. We studied the global conduits through which yellow fever virus can spread, and the potential for new yellow fever outbreaks to occur in the world’s urban areas.”

About 15 percent of people who get yellow fever develop serious illness that can be fatal, according to the U.S. Centers for Disease Control and Prevention (CDC).

Authors said the work involved separating the world into three types of places: places where yellow fever virus is established; areas that appear suitable for yellow fever virus transmission but where it has not yet been seen; and non-endemic areas where there is no yellow fever virus and the environment appears unsuitable for it to spread.

Investigators learned 89 percent of travellers departing from yellow fever-endemic areas to other yellow fever-endemic areas were required to provide proof of vaccination upon entry; less than 35 percent of travellers departing yellow fever-endemic areas for cities suitable for yellow fever virus transmission were required to provide proof of vaccination upon entry; and less than 25 percent of travellers who departed from areas of the world where there is no yellow fever virus for areas that are endemic with yellow fever virus were required to provide proof of vaccination upon entry.