Assessing the potency of oral polio vaccine kept outside of the cold chain during a national immunization campaign in Chad

This study is the first systematic documentation of the potency of monovalent oral polio vaccine type 3 (mOPV3) kept at ambient temperatures during a polio immunization campaign in Chad. During the study test vials were exposed to temperatures of up to 47.1 °C, and kept outside of the 2–8 °C range for a maximum of 86.9 hours. Post-campaign laboratory testing confirmed that the test vials were still potent, and in conformity with the defined release specifications. Further, the Vaccine Vial Monitors performed as expected, giving an early warning indication of when cumulative exposure to heat reached levels that may have negatively affected the vaccine's potency. This study provides proof-of-concept evidence that certain types of OPV remain potent and thus can be kept, for limited periods of time, as well as administered at ambient temperatures.

► we assessed the potency of mOPV3 kept at ambient temperatures during a polio vaccination campaign in Chad
► 20 vials were exposed to temperatures of up to 47.1 ∘C, and kept outside 2–8 ∘C range for up to 86.9 hours
► laboratory tests confirmed that all vials still met the potency release specifications - VVMs performed as expected, giving an early warning when cumulative levels of heat could have affected potency
► certain types of OPV can be kept at ambient temperature for limited periods of time, provided a VVM is used.