International collaborative assay of the international reference preparation of anti-yellow-fever serum.

A yellow fever immune serum was established in 1962 by the WHO Expert Committee on Biological Standardization as the International Reference Preparation of Anti-Yellow-Fever Serum, intended to serve as an immune reference serum in the mouse protection test used in the control of yellow fever vaccines.Before its establishment as the International Reference Preparation, the proposed material was assayed in eleven laboratories in ten countries against a number of other immune and non-immune sera, and was found stable. Neutralization test results were consistent and the relative potency was sufficiently high. This paper not only reports on the collaborative assay, but also discusses errors in the testing method and problems connected with the distribution of mouse deaths during the observation period and with the preparation of dilutions.