Interim Guidance, published 11 January 2021. The cold chain is necessary to prevent damage to vaccines caused by heat exposure. However, improper use of cold chain equipment may cause damage to freeze-sensitive vaccines (i.e. those vaccines containing alum adjuvant or oil-emulsion adjuvant). Studies conducted in several countries with hot and cold climates show frequent occurrences of sub-zero temperatures in the cold chain. The most common cause of exposure to freezing temperature is the failure to correctly condition ice packs prior to transport. Vaccines that are inadvertently frozen lose potency, increase wastage rates and increase the risk of adverse events following immunization (AEFI). Vaccine carriers protect vaccine potency during immunization sessions and transport to outreach sites. This guidance document is intended to help inform which type of vaccine carrier to select based on local context, to maintain vaccine quality, especially at service delivery points.