Caution needed in using oral polio vaccine beyond the cold chain: Vaccine vial monitors may be unreliable at high temperatures

摘要

Background & objectives: Stabilized live attenuated oral polio vaccine (OPV) is used to immunize children up to the age of five years to prevent poliomyelitis. It is strongly advised that the cold-chain should be maintained until the vaccine is administered. It is assumed, that vaccine vial monitors (WMs) are reliable at all temperatures. WMs are tested at 37degC and it is assumed that the labels reach discard point before vaccine potency drops to >0.6 log10. This study was undertaken to see if WMs were reliable when exposed to high temperatures as can occur in field conditions in India. Methods: Vaccine vials with WMs were incubated (10 vials for each temperature) in an incubator at different temperatures at 37, 41, 45 and 49.5degC. Time-lapse photographs of the WMs on vials were taken hourly to look for their discard-point. Results: At 37 and 41degC the WMs worked well. At 45degC, vaccine potency is known to drop to the discard level within 14 h whereas the WM discard point was reached at 16 h. At 49.5degC the WMs reached discard point at 9 h when these should have reached it at 3 h. Conclusion: Absolute reliance cannot be placed on WM in situation where environmental temperatures are high. Caution is needed when using 'outside the cold chain' (OCC) protocols.