Mitigating yellow fever vaccine associated viscerotropic disease in older travellers

In the 1930s, the development of a vaccine for humans toprevent or interrupt outbreaks of yellow fever,an acute viral haemorrhagic illness that is endemic in tropicaland sub-tropical areas of Africa, and Central and South America and in Trinidad, was hailed as a breakthrough. Early yellow fever vaccines were,because of theirtendency to cause neurotropic side effects,eventually replaced by the live attenuated vaccines used globally today. Using the17D-204 or 17DDstrainsof attenuated yellow fever virus as a backbone, these modern dayvaccines are acknowledged to be amongst the most effective and immunogenic vaccines ever produced ;1one dose is now considered enough, in most healthy individuals, to confer lifelong immunity.2Nevertheless, this remarkablevaccine,which is generally considered safe,hasover the past two decades,been dogged with a rare and worrisome side effect profile; seven cases of multiple organ system failure following yellow fever vaccination were identified in a review of adverse events (AE) occurring between 1996-2001.3Two separate serious AEprofiles occurring(almost exclusively)in first time vaccinerecipients, are recognised; Yellow Fever Vaccine Associated Neurologic disease [YEL-AND], which can occur two to 56 days after vaccination[RR 0.8 per 100 000 doses distributed]and Yellow Fever Vaccine Associated Viscerotropic Disease [YEL-AVD] which can occur one to eighteen days post-vaccination [RR 0.3 per 100 000 doses distributed], manifesting with fever and multi-organ failure, essentially mimicking the naturally acquired infection. Such serious AEare reported in all age groups but the reporting rate for both YEL-AND and YEL-AVD increases in persons aged 60 years and above.