Global Vaccine Safety

Yellow fever vaccine safety

Extract from report of GACVS meeting of 2-3 December 2004, published in the WHO Weekly Epidemiological Report on 7 January 2005

GACVS has previously reviewed the safety of yellow fever vaccines, with particular reference to viscerotropic disease and other serious adverse events.1 To date, 23 confirmed or probable cases of viscerotropic disease following the use of 17D yellow fever vaccine have been reported globally with case onset from 1996. Altogether, 14 (61%) of the 23 cases have been fatal. All cases were reported after the primary yellow fever vaccination. Recent risk estimates for yellow fever vaccine-associated viscerotropic disease are consistent with previous estimates from the United States, ranging from 0.04 to 3 per million vaccine doses. A higher risk has been recognized in subjects aged over 60 years. Disease of the thymus gland has been recognized as a potential independent risk factor; 4 (17%) of the 23 known cases had a history of thymus disease. However, there is little knowledge of additional risk factors for viscerotropic disease because of its low incidence.

GACVS reiterates that particular care should be taken that the vaccine is received only by those travellers who are truly at risk of exposure to yellow fever. In addition, vaccine providers should give careful consideration to the risks and benefits for elderly travellers and should routinely enquire about a history of thymus disorder, irrespective of the age of the subject. Where a history of thymus disorder is reported, alternative prevention measures should be considered.

1. See No. 3, 2004, pp. 16-20

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