Potency of oral polio vaccine stored at distribution centers in Madras

This study was done with the objective to measure, monitor, and document the potency of oral polio vaccine and the storage conditions in the city of Madras for a period of one year from May 88. The Corporation of Madras which takes care of indenting and supplying the vaccine has 87 centers for storage and distribution. We took 12 samples a month from these centers by stratified random sampling technique adopting proportionate sampling. The samples were coded and sent to the laboratory. The investigator noted the storage conditions in a specially designed data card. Results were notified to the managers concerned. 122 samples were tested out of which 28 (23%) showed loss of potency (less than log 10(5.84]. The loss of potency is statistically significant in centers not having dial thermometer and where inappropriate carrier was used for transport of vaccine. It was least in Maternity and Child Health Centers probably due to the orientation of the personnel. The frequency of loss of potency was more in the beginning of the study and decreased as the study progressed. Monitoring of storage conditions and potency of vaccine along with periodic training and reorientation of health personnel are stressed.