The short-term safety of an effective and inexpensive new live attenuated Japanese encephalitis vaccine (SA14-14-2) was studied in a randomized trial, using block randomization. Of 26,239 children who were enrolled, half received the vaccine and half served as controls. Subjects were prospectively followed for 30 days for severe adverse events, such as encephalitis, meningitis, and ''all-cause'' hospitalization. No cases of encephalitis or meningitis occurred in either group. The upper 95% confidence limit for adverse events not occurring among subjects receiving their first dose was 4.1/ 10,000. Risk ratios and 95% confidence intervals for other adverse events were 0.70 (0.43-1.15) for all-cause hospitalization, 0.91 (0.37-2.22) for seizure, and 0.79 (0.56-1.11) for fever lasting §3 days. These data attest to the short-term safety of the SA14-14-2 virus strain and the hamster kidney cell substrate.Japanese encephalitis (JE) is an important public health probwith a three-dose primary vaccination series recommended and yearly boosters administered in some countries. Thus, the exlem throughout a vast region of Asia. Conservative estimates place the annual incidence at ú35,000 cases, mostly in children pense and inconvenience of mouse brain-derived JE vaccine hinder immunization efforts. Adding to this difficulty has been [1]. Among these, ú10,000 die of JE, and an equal number develop permanent neurologic sequelae. JE is caused by a flathe occurrence of rare hypersensitivity and neurologic reactions, including encephalitis and encephalopathy, that have vivirus that circulates in zoonotic cycles involving many vertebrate species and is transmitted to humans by the bite of several been associated temporally (although not necessarily causally) with the existing vaccine [3]. mosquito species. Because of its zoonotic cycle, prospects for eradicating JE from the environment are dim, and universalIn 1988, an inexpensive (US $.75/dose) live attenuated primary hamster kidney-derived JE vaccine (SA14-14-2) was childhood vaccination is likely to remain essential for its control in the foreseeable future. licensed in China [4]. Prior to licensure, trials conducted in highly endemic areas indicated 95% efficacy after a single dose A killed mouse brain-derived JE vaccine with 91% efficacy (95% confidence interval [CI], 70%-97%) [2] that is manufac- [1,5]. A recent case-control study conducted in an area less endemic for JE showed 80% effectiveness (95% CI, tured by Biken (Osaka, Japan) is available internationally, although in insufficient quantities to meet the need worldwide.44%-93%) after one dose and 97.5% effectiveness (95% CI, 86%-99.6%) after two doses administered 1 year apart [6]. Similar mouse brain-derived vaccines are produced in limited quantities by manufacturers in other countries. The price of Some information concerning the safety of this vaccine is known. Results of a nonexperimental cohort study of the candiJapanese-produced JE vaccine in Asia is about US $5/dose, date vaccine were published in the Chinese li...
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