A small fraction of the yellow fever vaccine is just as effective as a full dose and can help protect more people during emergencies, a study conducted by Kemri scientists shows.
The results, published in The Lancet, confirm that one-fifth of the standard dose is enough.
There’s no cure for yellow fever, but a single dose of the vaccine protects a person for life.
However, there are often shortages of the vaccine because it takes about 12 months to produce. It is also difficult to predict the quantities that will be needed each year to respond to outbreaks.
“The use of fractional dosing could expand the outbreak stockpile up to five times, and therefore will be a crucial back-up tool in case of vaccine supply shortage during yellow fever outbreak response,” the study says.
The last case of yellow fever in Kenya was reported in 2016 in two Kenyan men who worked in Luanda, Angola.
None had been vaccinated against yellow fever prior to travelling to Angola.
The current study was led by Doctors Without Borders research arm Epicentre, and conducted by the Kenya Medical Research Institute, Institut Pasteur de Dakar, and the WHO, in Mbarara (Uganda) and Kilifi between November 2017 and February 2018.
“This study means that treatment providers can now rest assured that giving people smaller doses of any of the World Health Organization prequalified yellow fever vaccines will protect the person in front of them while helping to keep even more people safe,” said Myriam Henkens, MSF international medical coordinator.
During the study period, researchers administered either one-fifth or a standard dose of yellow fever vaccine to 960 adults between the ages of 18 and 59 years.
People receiving one-fifth of the dose were found to have an immunological response that was considered non-inferior to the standard dose.
“Thanks to these results, the current WHO policy on fractional doses of yellow fever vaccines in times of shortages during an outbreak can be expanded to all prequalified vaccines,” the authors said.
The study used the four existing WHO-approved vaccines and said fractioning works across all of them.
Yellow fever is spread by mosquitoes and causes acute viral haemorrhagic fever that kills 30,000 people per year, most of them in Sub-Saharan Africa.
While the infection is asymptomatic or causes only mild symptoms in many people, a small percentage of those infected experience a more toxic stage of the disease that can cause internal bleeding and severe damage to the liver and kidneys.
Approximately half the people who enter this stage of yellow fever die within a few days.
(edited by o. owino)