Fewer than a quarter of airplane passengers traveling to countries where yellow fever is endemic were required to show proof of vaccination against the disease upon arrival, when they were traveling from countries where the disease is not transmitted locally, according to a report released this week by the World Health Organization. The finding, the authors write reveals “a significant policy gap,” that leaves travelers vulnerable to infection, and other countries then, vulnerable to possibilities of the virus being imported.
Their report: International travel between global urban centres vulnerable to yellow fever transmission is based on an analysis of data from all commercial airports within about 125 miles — or 200 kilometers — of areas where yellow fever is transmitted locally. The analysis comes after an outbreak that developed following the first locally transmitted case recorded in Angola in more than a decade, that spread across that country’s 18 provinces causing 377 deaths, and into Kenya and the Democratic Republic of the Congo, where 121 people died as a result of the ensuing outbreak. Climate change, accelerated urbanization, and increased air travel for trade and tourism are multiplying opportunities for mosquito-borne viruses that include dengue, chikungunya and Zika as well as yellow fever to spread globally, the authors note. Of those, yellow fever is the only virus preventable through an effective vaccine. Their report comes as the U.S. Centers for Disease Control and Prevention release data showing illnesses spread by ticks fleas and mosquitos more than tripling in the United States during the last dozen years.
According to the WHO Bulletin report, an estimated 923 million people live in areas where yellow fever is endemic, in 25 countries and territories where the virus is endemic throughout, and 17 countries and territories where the virus is spread locally in only some areas. For their analysis, researchers used data on dengue virus transmission to additionally identify cities where yellow fever is not endemic but where vectors, climate and environmental conditions would support transmission of the virus. In 2016, according to the report, 45.2 million people traveled from yellow fever endemic areas to international destinations. Of them, 7.9 million, or a little more than 17 percent, had final destinations at airports within, or adjacent to places where the virus also is spread locally, and 11.7 million, or a little more than 25 percent traveled to places where the virus could be transmitted locally. Researchers found that 89 percent of those traveling from countries where yellow fever is endemic to cities in other countries where the virus is endemic throughout or in some areas, were required to show proof upon arrival that they had been vaccinated against the virus. Fewer than 35 percent of those traveling from areas where yellow fever is endemic to places that could support transmission of the virus were required to show proof of vaccination on arrival. Finally less than 25 percent of those traveling from non-endemic areas to cities where yellow fever is transmitted locally were required to show proof of vaccination to gain entry.
The findings indicate, the authors note, that national self-interest — raised when travelers pose risks of importing the virus, provides a stronger incentive for requiring vaccine proof upon entry than interest in protecting travelers, or the countries they might then export the virus to. The findings also point to an assumption, the authors note, that where yellow fever is not currently endemic, it never will be, an assumption belied by the outbreak in Angola.