Determination of Factors Affecting Bivalent (Type 1 and 3) Stability of Oral Poliomyelitis Vaccine

Background and objectives: After using of trivalent oral poliovirus vaccine (OPV) for a long time in Iran, in recent years, due to the eradication of type 2 of poliovirus, a bivalent vaccine containing types 1 and 3 is used. Since it is a highly thermo labile vaccine strain of poliovirus, it should be stored under the recommended temperature. Because in vaccine storage and transportation, the cold chain may not be achieved in Iran tropical weather conditions, the potency of this vaccine may be subject to change. Methods: The purpose of this study was the stability evaluation of bivalent oral poliovirus vaccine produced by Razi Institute in Iran for stability study of vaccines to ensure constancy of virus at different temperatures and intervals freezing/defrosting cycles (stress tests). Three consecutive batches produced during full-scale production were sampled randomly. All quality control tests in the form of stability studies were done on vaccines stored at -20, 2-8, 22-25 and 35-37ºC in specific time intervals and 10, 20, 30, 40 and 50 freezing/defrosting cycles. Results: The findings indicate the stability of this vaccine in different situations. The results also showed the effects of the environment affecting factors on the potency of the vaccines and determined the correlation between the VVM grade and the vaccine potency. Conclusion: Important observations of the vaccine distribution network at different transit levels and the correlation of VVM grade and vaccine potency and freezing/defrosting are discussed in this study which will be of help to the vaccine program team.