The yellow fever ‘booster’ vaccination given 10 years after the initial vaccination is not necessary, according to the World Health Organization (WHO).
The WHO's group of experts on immunization believes one dose of vaccination is enough to provide life-long immunity against yellow fever.
"This is very important because it will allow endemic countries currently using booster doses in their schedule to consider alleviating this schedule, and it also has implications for travelers," said Dr. Philippe Duclos, a senior health advisor in the department of Immunization, Vaccines, and Biologicals at the World Health Organization.
The information was published in an article Friday, noting that during the 80 years since yellow fever vaccination began, there have been only 12 known cases where someone who had been vaccinated developed the disease. In all 12 cases, they developed yellow fever within five years of the vaccine, before the 10-year booster would have been administered.
Yellow fever is an acute viral hemorrhagic disease that is transmitted by infected mosquitoes. It is endemic to 44 countries in tropical areas of Africa and the Americas.
Duclos says Friday's news will have the greatest impact in South America, where many countries have been administering the booster. In many African countries, he says the booster is not common practice.
"The impact will be mostly for countries in South America," he said. "For countries in Africa, it will be very reassuring for them. It will allow a vaccine, which is not in large supply, to be used where it is most needed."
Every year there are an estimated 200,000 cases of yellow fever around the world. But Duclos says the WHO's most recent figures suggest that the numbers in endemic countries in Africa are much higher than that - with up to 1.9 million people infected every year and up to 68,000 deaths.
He says the revised number is due in part to more precise estimates. In the past two decades, the number of yellow fever cases worldwide has increased, he says, because of things like declining population immunity to infection, deforestation, urbanization, population movements and climate change.
A big problem, according to Duclos, is that in a number of African countries, immunization schedules are not in place.
"In Africa there are still countries that have not introduced the vaccine in their routine schedule and also countries that have not done catch-up vaccination campaigns to take care of the pool of susceptibles in their population, so the risk is there," he said.
Duclos says by the end of 2011 nine African countries were not carrying out routine vaccinations, including Sudan, Uganda, Somalia, and Ethiopia.