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Infants vaccinated against yellow fever might still require a booster vaccination, study by RKI and others suggest

An African child gets a Yellow fever vaccination. Source: C. Onuekwe / WHO

Yellow fever is a life-threatening viral disease transmitted by mosquitos. Thirty-four countries in Africa and 13 in the Americas are at risk of yellow fever transmission; Angola and Brazil have suffered from severe yellow fever outbreaks in recent years. Yellow fever can be prevented thanks to safe and efficacious vaccines, which provide long-lasting immunity against the disease.

Since 2013, the World Health Organization (WHO) has recommended a single dose of the vaccine for life-long protection. In those areas where yellow fever is endemic, the vaccine is routinely given to infants aged 9 to 12 months. However, the duration of the protective immunity conferred by yellow fever vaccination in this age group is less well known than for adults or older children. The Strategic Advisory Group of Experts (SAGE) on Immunization , the main advisory group to WHO for vaccines, has identified this as a knowledge gap, and called for further investigations in this field of study.

A new study published in The Lancet Infectious Diseases by researchers from the Robert Koch Institute (Berlin, Germany), the Institut national de la santé et de la recherche médicale (Inserm, Toulouse, France), PATH (Seattle, USA), the National Institute for Public Health Research (Bamako, Mali), and the Navrongo Health Research Centre and Research Laboratory (Navrongo, Ghana), sought to confirm whether children vaccinated at age 9–12 months develop long-term protective antibodies as enjoyed by those who receive the vaccine at a later age. The researchers focused on two children populations from Ghana and Mali where neutralizing antibodies against yellow fever virus had already been measured earlier, only four weeks after vaccination, in a previous study. In the present study, the researchers measured the response to the yellow fever vaccine on a much longer time scale of two to six years. They observed that the percentage of children with protective antibodies was in both groups much lower than anticipated. The protective antibodies showed a substantial decrease from the seroprotection values at the four-week mark. In one group, more than half of the children displayed no neutralizing antibodies against yellow fever virus only two years after vaccination. The study was carried out with support from the Wellcome Trust Foundation.

These findings suggest that children vaccinated against yellow fever at a very young age may still require a booster vaccination. The new data could contribute to drawing up an ideal revaccination strategy against yellow fever that will achieve robust, lifetime protective immunity in those initially vaccinated as infants, and remove the risk of deadly yellow fever outbreaks in their communities.

Date: 20.09.2019