An international collaborative study of the assay of the potency of poliomyelitis sera.

As a first step towards the standardization of poliomyelitis vaccine, the neutralizing antibody titres of ten test antipoliomyelitis sera were measured in nine laboratories in different countries in comparison with a reference preparation. A standard neutralization test was not used by all laboratories and in general those neutralizing the serum-virus mixtures at a temperature of 37 degrees C obtained higher titres than those laboratories using lower temperatures. When the potencies of the test sera were calculated, in terms of the reference preparation, there was good agreement by all laboratories with sera of similar neutralizing capacity. The reference sera used in this study have proved useful for obtaining relative potencies for poliomyelitis sera of different neutralizing capacity and of different origin. These potencies have been shown to vary much less from one laboratory to another than did the uncorrected titres.For technical reasons, these reference preparations are not considered ideal for international standard preparations, and new sera have been prepared for this purpose.