The Oral Polio Vaccine (OPV) is the most heat-sensitive of all vaccines used in the Expanded Programme on Immunization (EPI). It must be stored at -15°C to -25°C at the national and provincial level. However, at the district/peripheral level, OPV can be stored at +2°C to +8°C for short periods. The option -15°C to -25°C is the standard cold chain requirement. Mismanagement of cold chain is a leading cause of vaccine failure — a Head Nurse must strictly monitor this.