RESUMEN
The stability of four samples of oral polio vaccine received from different laboratories stored at -20°C, 5°C, 25°C, 31°C and 37°C for different intervals of time was studied. The virus titration were performed by the standard method in tissue culture microtitre plates. There was a little loss in virus titre when samples were kept at -20°C and 5°C for 8 days and 25°C for four days, where as the samples exposed to 25°C for 30 days and 31°C for 12 days showed almost 50% loss in virus titre. The sample subjected to 10 cycles of freezing and thawing did not show any loss in virus titre. Oral polio vaccine stabilized with magnesium chloride or sucrose is quite a stable vaccine and maintenance of a proper cold chain is recommended for the delivery of a potent vaccine in countries with high ambient temperature