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

Background and objectives: in recent years, due to the eradication of type 2 poliovirus, a bivalent vaccine containing types 1 and 3 is used in iran. since it is a highly thermolabile vaccine, it should be stored at a recommended temperature. since cold chain may not be applied in iran’s tropical weather conditions, potency of the vaccine may be subjected to change. therefore, we evaluated the effective factors on the potency of this vaccine. methods: we evaluated stability of a bivalent oral poliovirus vaccine produced by razi institute of iran to ensure consistency of virus at different temperatures (-20, 2-8, 22-25 and 35-37 ºc), time intervals and freeze/thaw cycles. three consecutive batches produced during full-scale production were randomly sampled. results: at -20 oc, there was no change in vaccine vial monitor (vvm). the potency of the samples exposed to 2-8 oc for 60 days and to 22-25 oc for five days met the specification. the mean potency of the samples was 6.17, 6.00, 5.83, 5.75 and 5.54 (log ccid50/dose) after 10, 20, 30, 40 and 50 freeze/thaw cycles, respectively. in addition, the mean degradation of vvm was 0, 23.33, 60 and 100% for samples exposed to -20, 2-8, 22-25 and 35-37 oc, respectively. conclusion: the results indicate the effects of environmental factors on the potency of the vaccines and the correlation between the vvm grade, color change and the vaccine potency for programming vaccine distribution networks at different transit levels. based on the results of our study, the best temperature for maintenance and transportation of bivalent oral poliovirus vaccine is -20 oc. furthermore, freeze/thaw cycles lower the potency of the vaccine and change the vvm grade significantly.