Emergency outbreaks of yellow fever virus make comeback despite availability of an effective vaccine since the 1930s
Yellow fever is back with 200,000 lives at risk per year
Before the development of a life-saving vaccine in the 1930s, the yellow fever virus was responsible for devastating epidemics in large cities in Africa, South, Central & North America and Europe.
Almost a century later, yellow fever is back, striking an estimated 200,000 people per year and claiming 30,000 lives.
Since the eighties, cases are occurring in areas that had previously not experienced outbreaks, such as southern Brazil, northern Argentina and central Paraguay, or that had no confirmed cases in decades - the Central African Republic, Chad, Congo, Liberia and Sierra Leone and more recently in the Darfur region in Sudan.
Rapid urbanisation has exacerbated the issue by concentrating non-immune populations in settings where yellow fever virus thrives. City areas provide fertile breeding grounds for mosquito larvae: stagnant water collects in water containers, cans, tyres etc. Overcrowded housing does the rest, accelerating the viral effect.
Yellow fever's recent resurgence is especially pronounced in West and Central Africa, where mass vaccination campaigns from 1933-61 had effectively resulted in the disappearance of the virus.
This alarming trend started in equatorial Africa with a 1990 epidemic in Cameroon before spreading across the region. By 2005, failure to immunise successive birth cohorts through routine infant immunisation had led to an estimated 206,000 yellow fever cases and 52,000 deaths in West Africa's 12 highest risk countries.
As an acute viral haemorrhagic disease transmitted by mosquitoes, yellow fever causes devastating epidemics in areas where infected mosquitoes can come in contact with non-immunised populations. Up to 50% of people severely affected by yellow fever will die
Yellow fever virus poses the greatest threat to 900 million people in more than 45 endemic countries - 34 in Africa and 13 in Central and South America. Together, deforestation, urbanisation, climate change and low population immunity have contributed to its re-emergence since the 1980s.
Yellow fever can be prevented by a safe, affordable and highly effective vaccine. One injection protects an individual for at least 35 years, and possibly for life.