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.
2015 has seen a sudden spike in the number of cases of Hepatitis A in Hong Kong. Compared to the annual average of about 44 cases seen over the last five years, the first 14 weeks of 2015 has already seen a spike in cases of Hepatitis A, with the reported number standing at 64 at the last reckoning.
In response to the media queries on this issue, the Department of Health issued the following response on April15, 2015:
“Hepatitis A is a statutory notifiable infectious disease in Hong Kong. CHP will carry out epidemiological investigations for every cases of hepatitis A in due course to understand whether the patients had consumed high risk-food like shellfish and berries during the incubation period, and will implement appropriate preventive and control measures.
As of yesterday (14 Apr 2015), CHP has recorded 64 cases of hepatitisA infection this year, comprising 32 males and 32 females aged 11 to83. All patients are in stable condition with no death recorded. Amongthem, only 19 cases had consumed various types of berries, while only8 of them had consumed blueberries during the incubation period.Epidemiological investigations so far did not show sufficient evidence of epidemiological linkage between the increase of hepatitis A cases and eating blueberries.”