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).
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