An evaluation of cold chain in Maharashtra & Karnataka states by potency testing of field samples of oral poliovirus vaccine.

The cold chain for oral poliovirus vaccine was monitored in Maharashtra and Karnataka by potency testing of vaccine vials collected from various stages of the delivery system. Results showed that cold chain maintenance improved in the state of Maharashtra within a period of three years as the monitoring began in 1987. Of the 6289 samples of trivalent OPV collected from all 30 districts of the state during 1990 to 1992, 5834 (92.8%) had retained virus titre of at least 10(5.81) TCID50/dose. 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 Karnataka could be demonstrated by plotting virus titre of samples of individual batches collected from different outlets. It was concluded that potency retesting of OPV samples for cold chain monitoring will ensure proper storage, transport and use of potent vaccine in the field.