Problems of influenza virus vaccine standardization.

The lack of reliable laboratory methods of determining the antigenicity of inactivated influenza virus vaccines prompted a reinvestigation of the reproducibility of the tests used for measuring the antigenic content of influenza vaccines, namely, the CCA and mouse potency tests.The data obtained in the second part of the mouse potency test, i.e., the neutralization test performed either in mice or in embryonated eggs, statistically demonstrated protective differences between 2 vaccines differing in antigenic mass by as little as 2-fold. However, the dependence upon a single egg or mouse neutralization test to provide the correct vaccine/reference ratio assumed more than "biological" variation would allow. Further, the test was long and tedious and it would be impracticable to perform the number of tests needed to obtain statistically significant results. Thus, the extreme variability observed between individual mouse potency tests and the impracticability of performing this test in statistically sufficient numbers precluded its use for measuring antigenic content of inactivated influenza vaccines.The simpler CCA test, on the other hand, did provide the reproducibility required for the correct determination of the vaccine/reference ratio once a stable CCA reference vaccine was prepared. This test was easily reproducible and results obtained were sufficient to allow a meaningful and reliable conclusion to be drawn with respect to vaccine potency.The problems of measuring the relative content of several components in multivalent vaccine preparations and of finding a test which positively correlates with vaccine potency in man, however, remain unsolved.