“Cold chain” refers to the process used to maintain optimal conditions during the transport, storage, and handling of vaccines, starting at the manufacturer and ending with the administration of the vaccine to the client. The optimum temperature for refrigerated vaccines is between +2°C and +8°C. For frozen vaccines the optimum temperature is -15°C or lower. In addition, protection from light is a necessary condition for some vaccines.
Proper storage temperatures must be maintained at every link in the chain.
Vaccines are sensitive biological products which may become less effective, or even destroyed, when exposed to temperatures outside the recommended range. Cold-sensitive vaccines experience an immediate loss of potency following freezing. Vaccines exposed to temperatures above the recommended temperature range experience some loss of potency with each episode of exposure. Repetitive exposure to heat episodes results in a cumulative loss of potency that is not reversible. However, information on vaccine degradation is sparse and multipoint stability studies on vaccines are difficult to perform. In addition, information from manufacturers is not always available, so it can be difficult to assess the potency of a mishandled vaccine(1).
Maintaining the potency of vaccines is important for several reasons.
There is a need to ensure that an effective product is being used. Vaccine failures caused by administration of compromised vaccine may result in the re-emergence or occurrence of vaccine preventable disease.
Careful management of resources is important. Vaccines are expensive and can be in short supply. Loss of vaccines may result in the cancellation of immunization clinics resulting in lost opportunities to immunize.
Revaccination of people who have received an ineffective vaccine is professionally uncomfortable and may cause a loss of public confidence in vaccines and/or the health care system.
An estimated 17% to 37% of healthcare providers expose vaccines to improper storage temperatures. Refrigerator temperatures are more commonly kept too cold rather than too warm(2,3). One study involving site visits showed that 15% of refrigeration units had temperatures of +1°C or lower(3).
Temperatures falling outside the recommended range require immediate action to avoid loss of product.
When a cold chain break is identified after a vaccine has been administered, consult your local public health office or immunization program* for advice. The type of vaccine, duration and temperature of the exposure will be taken into account when assessing the situation. Serological testing or revaccination may be suggested(4).
Vaccines are sensitive biological products that may become less effective, or even destroyed, when exposed to temperatures outside the recommended range and/or on exposure to direct sunlight or fluorescent light.
Three main elements combine to ensure proper vaccine transport, storage, and handling.
Each of these elements will be addressed in subsequent sections.
The “shake test” was one method previously used as an indicator that a liquid vaccine was inappropriately frozen. A positive shake test is the formation of granular particles which show up in the liquid upon shaking the vaccine after the vaccine was frozen and then thawed.
The shake test is not a reliable method of testing vaccine potency because a positive shake test may or may not occur after a liquid vaccine has been frozen.
Grassby PF. Safe storage of vaccines: problems and solutions. Pharm J 1993;251:323–327.
Gazmararian JA, Oster NV, Green DC et al. Vaccine storage practices in primary care physician offices: assessment and intervention. Am J Prev Med 2002;23(4):246–53.
Bell KN, Hogue CJR, Manning C et al. Risk factors for improper vaccine storage and handling in private provider offices. Pediatrics 2001;107(6):1–6.
National Advisory Committee on Immunization. Canadian immunization guide. 7th ed. Ottawa, Ont.: Public Health Agency of Canada, 2006. (Minister of Public Works and Government Services Canada. Cat. No. HP40-3/2006E).
* Including local, regional, provincial, territorial, or federal health departments, or other jurisdictional immunization programs.