A Collaborative Study on KoreanStandard JE Vaccine for Potency Assay

The objective of this collaborative study was toestablish a Korean standard of Japanese encephalitis (JE)vaccine (mouse brain-derived, formalin-inactivated) for potencyassay. A candidate preparation proposed as a Korean standardwas provided by GreenCross Vaccine, and six laboratories,including one national control laboratory and five manufacturersof JE vaccine, participated in the study. The potency of thecandidate preparation and a reference standard obtained fromJapan was estimated by mouse immunogenicity assay usingthe in vitro plaque reduction neutralization test (PRNT). Theresults of 72 assays conducted by the 6 laboratories showedthat the overall mean potency estimate of the candidate preparationwas 2.455 log median plaque reduction neutralizationantibody titer per 0.5-ml dosage administered twice in mice at7-day intervals, and that the mean potency ratio of thecandidate preparation relative to the reference standard was1.074. The potency estimates were quite variable amonglaboratories irrespective of the preparation. The variability ofassays assessed by Z scores and coefficient of variation (CV)were in general within the level of acceptance (Z scoreswithin ±3 and CV ≤15%). Therefore, we concluded that thecandidate preparation would be suitable as a national standardfor testing the potency of JE vaccine (inactivated). KCI Citation Count: 2