A Method Applicable to the Standardization of Influenza Virus Vaccines.

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Abstract
A procedure applicable to the standardization of influenza virus vaccines is described. The procedure, referred to as the antigenic extinction titration, determines the highest dilution of antigen capable of inducing the formation of a demonstrable amt. of virus-neutralizing antibody in the pooled serum of groups of 10 mice. The test for neutralizing antibody is carried out in ovo and may, therefore, be used in those instances in which the strain of virus that may be included in a vaccine has been adapted only to the chick embryo and is not pathogenic for mice. The use of chick embryos rather than mice as the indicator medium for virus neutralization offers the advantage of completion in 2 days rather than 10 days, applicability to egg-adapted strains and sharpness of results, as well as being less costly. The importance of maintaining the identity of virus in vaccine and virus used as test antigen for measuring the antibody response induced by immunization has been illustrated and discussed.