The term cold chain refers to all the material, equipment and procedures used to maintain biological products within the required range of 2° to 8°C at all times during handling, storage, and transport. Breaks in the cold chain can result in the lack of vaccine effectiveness, undue vaccine failures and an increased rate of local reactions after vaccine administration.
Many biologicals can be inactivated by exposure to heat or freezing. The specific effect of temperature on the potency of biologicals depends on the type of biological, and the temperature and duration of exposure. Inadvertent freezing can substantially reduce the potency of alum-adsorbed vaccines such as DPTP and Hepatitis B. Exposure to heat and light can compromise the stability of live virus vaccines, such as MMR.
Please see the attached document: Cold Chain Maintenance (PDF 60 KB) chapter from the Nova Scotia Immunization Manual, Department of Health for detailed information.