The authors thank Mrs J. Jacobson for editorial assistance. The authors state that they have no conflicts of interest. “
“We describe an allergic reaction to both mouse C646 molecular weight brain-derived BIKEN and Vero cell-derived IXIARO Japanese encephalitis (JE) vaccines in a single traveler. In the absence of the stabilizers and murine proteins in the BIKEN vaccine, a common factor in both vaccines is likely to be responsible, possibly JE virus antigen itself. Japanese encephalitis (JE) is a mosquito-borne flavivirus and the leading cause of vaccine-preventable encephalitis in Asia.[1] Less than 1% of humans infected with JE virus develop clinical disease, yet up to 30,000 symptomatic cases of JE are still reported annually and this

figure is probably an underestimate.[2] JE has a case-fatality rate of 20%–30%, and of those surviving, as many as 25%–50% may suffer from long-term neurologic or psychiatric sequelae.[2] There is no curative treatment for symptomatic JE and in endemic countries vaccination remains an important public health priority. The risk for travelers from nonendemic countries is estimated to

be in the region of one case per million travelers.[1] However, the risk for those staying in rural areas for long periods is estimated to be similar to that of the susceptible resident population and is considered an indication for vaccination.[2] Two JE vaccines have been available for use in the UK: an inactivated mouse brain-derived vaccine (JE-VAX/BIKEN [JE-MB]) and an inactivated Vero cell culture-derived vaccine (IXIARO [JE-VC]). An adverse safety profile and multiple reports of moderate to severe Venetoclax research buy hypersensitivity-type reactions associated with vaccination led to the cessation of JE-MB production by one manufacturer in 2006 (Sanofi Pasteur MSD), although this continues in Korea (Green Cross).[2, 3] JE-MB was prepared by intracerebral inoculation of neonatal Exoribonuclease mice with JE Nakayama-NIH strain.[4] Adverse events have been estimated to occur at a rate of 1–17 per 10,000 vaccines and included generalized urticaria,

angioedema, and respiratory distress.[5] These reactions have been attributed to the use of gelatin or thimerosal stabilizers or residual murine neural proteins, although none has been proven causative.[1, 5] The WHO placed a high priority on the development of new vaccines and in 2009 the JE-VC (IXIARO) vaccine completed Phase III trials. This vaccine is an inactivated, alum adjuvanted vaccine, manufactured in cultured Vero cells from the SA14-14-2 strain, and is formulated in serum-free medium without gelatin, thimerosal, or other stabilizers.[6] Noninferiority to the JE-MB vaccine by immunogenicity and antibody titers was demonstrated with a favorable safety profile.[7] Adverse events were generally mild, and this vaccine has replaced JE-MB vaccine in clinical use in adults and is close to doing so for children.[7] We describe a case of allergic reaction to both the JE-MB (BIKEN) and the JE-VC (IXIARO) vaccines in one patient.