Are potency tests for tetanus vaccines really necessary?

There is no simple relationship connecting the antigen content to the immunogenic potency of tetanus vaccines and the need for potency tests therefore remains inescapable. However, the quantal response methods of assay presently used for the measurement of potency appear to use unnecessarily large numbers of animals and substantial reductions could be made, particularly in the control of combined vaccines, if toxic challenge were replaced by in vitro titration of antitoxin.