Wednesday, 10 October 2012

Yellow fever resurgence : impact of mass vaccination campaigns

Historically yellow fever (YF) has caused devastating epidemics in Europe, Africa, South, Central and North America, but, for unknown reasons, yellow fever has not spread to Asia yet. The development of the live attenuated 17D vaccines in the 1930s was a turning point in the history of the disease. One dose of YF vaccine provides protection for at least 10 years and possibly lifelong. The vaccine is considered to be very safe.
Successful attempts to control yellow fever through compulsory immunization took place in the beginning of the 20th century : in some French speaking African countries (Benin, Burkina Faso, Cameroon, Chad, Cote d'Ivoire, Congo, Gabon, Guinea, Senegal, Togo) mass vaccination campaigns were carried out between 1933 and 1961 and resulted in the gradual disappearance of the disease.
Until the early 1990s, almost 30 years after the end of the mass preventive immunization campaigns, yellow fever remained only very sporadically active in the countries that benefited from those campaigns. However, during the same period, countries such as Ethiopia, Gambia, Ghana, Guinea Bissau, Liberia, Nigeria and Sierra Leone, which did not benefit from mass vaccination campaigns, experienced large epidemics.
The interruption of regular mass vaccination campaigns in Africa has played a major role in the current resurgence of yellow fever. The resurgence began in equatorial Africa, with the 1990 epidemic in Cameroon (173 cases) in which 79% of the victims were children aged under 10 years. The disease then struck in West Africa and since 1995 this has been the region most affected by yellow fever.