Many vaccines have highly specific storage requirements that if not met can reduce their potency significantly, even rendering them completely ineffective. Vaccines must be stored correctly from the moment they are manufactured until they are ultimately administered, and this is the shared responsibility of the manufacturer, distributor, and healthcare provider.
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What are the most common storage conditions?
The vast majority of vaccines should be stored at between 2-8⁰C in a refrigerator, with a preferred average of 5⁰C, though some should remain frozen in a range between -15 to -50⁰C. Additionally, many should be protected from light and are packaged appropriately, as UV-light can damage them.
Many live-virus vaccines can tolerate freezing temperatures and rapidly deteriorate once defrosted, while inactivated vaccines more commonly require stable temperatures of 2-8⁰C and are damaged at temperature extremes. The commonly administered measles, mumps, rubella (MMR) vaccine can be stored either frozen or refrigerated, while the MMRV vaccine that also contains the live varicella virus must be frozen.
In some cases, manufacturers may recommend storing the concentrated form as provided at one temperature and the prepared diluted form, if any such steps are necessary, at another, though generally the latter should not be prepared more than 30 minutes in advance. In cases where a frozen vaccine must be prepared then most manufacturers recommend slowly defrosting in a refrigerator. For example, all vaccines that contain varicella, the live virus chickenpox vaccine, should be stored frozen but can be defrosted in a refrigerator for 72 hours before use.
A major review of the literature published before 2007 by Matthias et al. (2007) found that between 75-100% of vaccines are inadvertently exposed to freezing temperatures at some point in the cold-chain, the time between manufacture and administration. The group recommended several fixes including the use of cool water packs rather than ice packs, improved training for vaccine handlers, and taking advantage of the heat stability of many vaccines, where allowing them to warm above 8⁰C for a limited time may be preferable to freezing.
What steps can be taken?
The CDC recommends that each of the participants of the cold chain develop and maintain a thorough written plan for the ordering, acceptance, handling, and storage of such products, including accounting for emergency storage locations should there be a power outage or similarly urgent situation.
Several studies have highlighted key issues in vaccine storage, with the most commonly found errors including the storage of vaccines past their expiration date, deep freezers being too warm (-14⁰C or higher), and refrigerators being too warm (over 8⁰C). Major risk factors have been identified, such as lacking a thermometer in freezers, and less commonly in refrigerators, or using a combination refrigerator/freezer, as the freezer compartment inside such devices keeps poor temperature homeostasis.
Additionally, the compartments frequently affect one another’s temperature, particularly in smaller appliances, where setting the freezer compartment to the desired -14⁰C lowers the fridge to below 2⁰C, damaging the refrigerated vaccines.
Preferably, all refrigerators and freezers should be free-standing and dedicated to the purpose. Most consumer appliances do not offer the stability in temperature required to store vaccines, both in terms of hourly fluctuations but also across seasons. The cooling coil accessible on the interior of many refrigerators also poses a potential hazard, and units with exposed coils are banned from storing vaccines in many countries.
Similarly, the walls, cooling vents, door, floor, and ceiling of refrigerators are more prone to temperature fluctuations than the center of the unit, where vaccines should be stored in full packaging.
Each unit should also possess an independent thermometer that is calibrated regularly, preferably with an external temperature display that can be viewed without opening the door. As a best practice, most storage locations are likely to utilize an automatic temperature logger so that historic temperatures can be reviewed, though this may be done manually where a digital option is not available.
Surge protectors and other electronic safety equipment should be utilized to lower the risk of interruption of power or loss of storage unit, and all inventory should be carefully logged taking special note of the expiration date.
As a practical point, the CDC additionally recommends not storing “sound-alike” or “look-alike” vaccines in the same location, to avoid the incorrect vaccine being selected. If a refrigerator must also store other biologics then the vaccines should be placed on the highest shelf to avoid contamination, and food or drink should never be stored in the same unit.
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Further Reading
A scaffolded vaccine approach for broader influenza protection