Attempt to curtail the observation period of mice in the tetanus vaccine potency tests

Curtailing the observation of mice challenged with tetanus toxin in potency test of tetanus vaccine would reduce the agony of mice from spastic paralysis. From the viewpoint of animal welfare, we investigated the feasibility of this measure. The potencies of 85 lots of vaccine obtained on the 4th day after challenge were compared with those obtained on the 7th day. No significant difference was found (P = 0.05), indicating that the observation period could be curtailed from 7 days to 4 days without impairing the assessment of the vaccine's potency.