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Evidence summaries

Vaccines for Preventing Japanese Encephalitis

Currently used vaccines to prevent Japanese encephalitis appear to be effective and to cause only occasional mild or moderate adverse events. Level of evidence: "B"

A Cochrane review [Abstract] 1 included 8 studies with a total of 358 750 subjects. These trials investigated two available and three pre-licensure vaccines. A two-dose schedule of the commercially available inactivated Nakayama vaccine provided protection of 95% (1 RCT, 95% CI 10% to 100%) for one year, while two doses of an unpurified precursor vaccine protected children by 81% (1 RCT, 95% CI 45% to 94%) in year one and by 59% (1 RCT, 95% CI 2% to 83%) in year two. Serious adverse events were not observed. Mild and moderate episodes of injection site soreness, fever, headache, and nausea were reported in less than 6% of children receiving inactivated vaccine compared to 0.6% of unvaccinated controls. One cluster-RCT compared the live-attenuated SA14-14-2 vaccine (widely used in China) with no intervention measuring adverse events. Fever was reported in 2.7% of vaccinees compared to 3.1% of controls, while 0.1% of both groups suffered diarrhoea or seizures. Four small pre-licensure RCTs assessing a genetically engineered vaccine and two cell culture-derived inactivated vaccines revealed high immunogenicity and relative safety.

Comment: The quality of evidence is downgraded by heterogeneity in interventions (different vaccines) and outcomes (some studies investigated efficacy and some immunogenicity).

    References

    • Schiøler KL, Samuel M, Wai KL. Vaccines for preventing Japanese encephalitis. Cochrane Database Syst Rev 2007 Jul 18;(3):CD004263. [PubMed]

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