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

Highlights ► 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.