Storing Vaccines in Cold Weather

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As winter is upon us, veterinarians are out and about performing routine preventive work, including immunization boosters. Maintaining vaccines at an appropriate temperature during transport, storage and administration is critical.

Credit: Thinkstock Keeping vaccines from getting too cold in winter might prevent some reactions.

Credit: Thinkstock Keeping vaccines from getting too cold in winter might prevent some reactions.

ou might have a refrigerator in your truck or use a cooler with multiple ice packs to maintain cold temperatures for your vaccines. But what happens when it is cold outside throughout your working day? What happens when you replace thawed gel packs with frozen packs laid directly on top of and beneath vaccine vials, resulting in over-chilling of vaccines? When is “cold” too cold for vaccines?

Some practitioners have observed that adverse vaccine reactions often occur in a particular group of vaccinates— for example, a group of horses at a single barn that received vaccine from the same group of bottles show localized reactions. Or a group of horses living in northern states in winter might have an unusually high reaction rate after vaccination.

When vaccines get over-chilled, adjuvants start to crystallize. The adjuvant will separate from the antigen to form a precipitate, which is not always visible in the bottle but can elicit local inflammation at the injection site. Killed vaccine is particularly sensitive to the effects of freezing.

While there haven’t been many formal studies on this concept, it is possible that such over-chilling—whether in the originating warehouse, during shipping, in your truck, or close to your clinic refrigerator’s freezer—might cause the vaccine to begin to thicken and gel. Administration of a frozen or semi-frozen vaccine product— even once “thawed”—could possibly incite vaccine reactions more often than if it had been stored at a consistent and desired cooled temperature.

Basic refrigerator temperatures range from 35-46 degrees Fahrenheit. It is a good idea to place a quality thermometer in the center of your cold storage container and to monitor it closely each day.

Killed vaccine should be maintained at a constant cool temperature within this range and in a dark location.

OHSA (Occupational Safety and Health Administration) requires that no foods or beverages be stored in the vaccine refrigerator, in part because opening and closing the refrigerator for access to consumables tends to cause fluctuations in the desired constant temperature. The Centers for Disease Control (CDC) advise against the use of dormitory-style refrigerators due to challenges in maintaining a constant and appropriate temperature; those units tend to cause freezing of vaccine even when used for temporary storage.

For vaccines transported in a cooler, it is important to layer some insulation (foam, bubble wrap) between the vaccine vials and the ice packs to prevent freezing. In winter climates, keep the cooler in the vehicle’s passenger area rather than in the bed of a truck or a veterinary unit.

This is a reminder to all of us to be cognizant not just about storage of vaccine during warm and hot weather, but also to consider the effects of over-chilling equine vaccines any time of year.

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