Yellow fever vaccine is recommended to all travelers who are planning a trip to countries endemic for the disease. The vaccine is relatively safe and effective and recently, there have been two isolated reports of a fatal and extremely rare complication arising from the YF vaccine, the Yellow Fever Vaccine associated Viscerotropic Disease (YEL-AVD). The CDC MMWR reported a case in Oregon, USA, and the Outbreak News Blog reported a case from Hong Kong.
YEL-AVD results from the uncontrolled replication of the vaccine virus, finally leading to multi-organ failure and has a reported mortality to the tune of 60%.
FIGURE from CDC Report: Yellow fever virus antigens (red) detected after immunohistochemical staining in tissue samples from various organs* of a patient who died from yellow fever vaccine–associated viscerotropic disease — Oregon, September 2014
* Sample A: myocytes in heart; sample B: fibroblasts in vascular wall in lung; sample C: kupffer cell in liver; sample D: fibroblasts and histiocytes in skin. (Immunoalkaline phosphatase with naphthol fast-red substrate and hematoxylin counterstain. Original magnifications: A = x400; B = x100; C = x400; D = x100.)
The CDC report further states that the risk of YEL-AVD is 0.4 per 100,000 doses of YF vaccine administered. The risk is increases with age: in patients older than 60 years it has a risk of 1/100,000 doses while those that, those who are older than 70 years have a risk of 2.3/100,000 doses administered. Almost a quarter of the first few cases of YEL-AVD that have been reported had a history of thymoma and it is estimated that the increased risk attributable to thyme disease persists even after thyme resection.