AN EVALUATION OF COLD CHAIN IN MAHARASHTRA AND KARNATAKA STATES BY POTENCY TESTING OF FIELD SAMPLES OF ORAL POLIOVIRUS VACCINE

The cold chain for oral poliovirus vaccine was monitored in Maharashtr a and Karnataka by potency testing of vaccine vials collected from var ious stages of the delivery system. Results showed that cold chain mai ntenance improved in the state of Maharashtra within a period of three years as the monitoring began in 1987. Of the 6289 samples of trivale nt OPV collected from all 30 districts of the state during 1990 to 199 2, 5834 (92.8%) had retained virus titre of at least 10(5.81) TCID50/d ose. In comparison, 72 per cent of the 1660 samples collected from the state of Karnataka during the same period were found to contain this minimum required virus titre. Defects in cold chain maintenance in Kar nataka could be demonstrated by plotting virus titre of samples of ind ividual batches collected from different outlets. It was concluded tha t potency retesting of OPV samples for cold chain monitoring will ensu re proper storage, transport and use of potent vaccine in the field.