Monday, 2 September 2013

Japanese Encephalitis (JE) vaccine

Neurological complications to vaccination against Japanese encephalitis.
Some JE vaccines are produced from infected mouse brains and contain small amounts of myelin basic protein. Neurological side effects in larger vaccine trials in Asia have been reported in 1-2.3 per million vaccinees. Statens Serum Institut is the only distributor of JE vaccine in Denmark, delivering 384 000 doses from 1983-96. In 1996, evaluation of initial symptoms and findings in 10 adult travellers from Denmark, who developed moderate-severe neurological symptoms within a few weeks of JE vaccination, was performed as well as follow-up magnetic resonance imaging (MRI) and clinical neurological examination. Three patients initially had symptoms varying from severe encephalitis-like illness to paraesthesia, double vision or parkinsonian gait disturbance. MRI showed severe atrophy of the corpus callosum with altered signal intensity indicating gliosis in one patient, another patient had several hyperintense spots located periventricularly in the white matter, while a third patient had spots with increased signals in the pons, the right substantia nigra and the occipital region. Acute disseminated encephalomyelitis (ADEM) is a possible explanation for these MRI changes, although multiple sclerosis is an alternative diagnosis in one or two of the patients. Another three patients had long-lasting headache, concentration difficulty or intellectual reduction. One man had afebrile convulsions, another gait instability and depression and one parkinsonism. A woman developed myelitis. If these findings are due to JE vaccination the frequency of neurological reactions to the vaccine is considerably higher than previously reported and in the future any minor neurological complaints occurring shortly after vaccination should lead to neurological examination and acute MRI scan should be considered.

Allergic mucocutaneous reactions to Japanese encephalitis vaccine.

Japanese Encephalitis Vaccine for Travelers: Exploring the Limits of Risk
Because of the possibility of delayed, but potentially serious, hypersensitivity reactions to JE vaccine (discussed in the next section), recipients of JE vaccine should remain where adequate medical care is available for up to 10 days after they receive the last dose [1].

The first set of adverse reaction reports were reported from Denmark, Australia, and Canada [34–36]. These reports described urticaria and angioedema that occasionally involved the face and lips. Respiratory distress was reported in 3 vaccine recipients. Of concern to travel medicine practitioners was the observation that the reactions were often delayed by several days to, possibly, 2 weeks, which meant that some reactions could occur in recipients of the vaccine who had already begun their travels. However, it should be noted that anaphylaxis—and the consequent risk of sudden death—has never
been reported in relation to the administration of Biken JE vaccine

Only 1 fatality was noted during surveillance of 110,000,000 doses of JE vaccine administered in Japan and the United States. A 3-year-old boy developed fever, cerebral edema, and coma 2 days after JE vaccination and died within 4 days of vaccination.

Adverse reactions to Japanese encephalitis vaccine in travellers.
46% of the vaccinees reported about no adverse events at all. 54% reported about one or more adverse effects. Local reactions at the injection site were observed by 209 vaccinees, while 65 reported about systemic side effects like headache, fever, dizziness and generalized rash. There was no significant difference following first or second injection of the primary immunization or the booster injection, respectively, regarding incidence, severity or type of side effects. 2.2% of the vaccinees reporting reactions sought medical advice and 1.8% were judged unfit for work for an average of 2.2 days. The amount of systemic reactions might indicate a potential hazard of serious anaphylactic reactions. Unlike hepatitis A. Japanese encephalitis is an extremely rare disease in travellers.

Systemic reactions in U.S. Marine Corps personnel who received Japanese encephalitis vaccine.
The overall hypersensitivity reaction rate among 14,249 U.S. Marine Corps personnel who received 36,850 doses of an investigational Japanese encephalitis vaccine was 10.3 per 10,000 doses; reaction rates were 16.1 and 10.3 per 10,000 doses for the first two doses, and 2.0 per 10,000 doses for the third. The reaction rate was 26.7 per 10,000 vaccinees. Of 38 reactors, 26 had urticaria and/or angioedema, and 11 had pruritus. Vaccine reaction intervals clustered within 48 hours for dose 1, but the median reaction interval for dose 2 was 96 hours. A history of urticaria or allergic rhinitis was associated with an increased probability of a vaccine reaction.

However, because animals, rather than humans, are the natural hosts, mass immunization cannot cut the risk of disease to those who are not immunized. Thus, the risk to tourists is no different in countries with routine JE immunization for children.

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