The accidental freezing of vaccines is a largely overlooked problem, despite the fact that many of the most common vaccines are freeze-sensitive.
More than 90% of all vaccines require a temperature-controlled supply chain (the “cold chain”) that begins with the manufacturer and ends with the administration of the vaccine to the patient. Typically, shipping and storage guidelines advise that vaccines and biologics remain between 2° and 8° Celsius, the temperature range from which stability data was historically derived.
By prioritizing protecting vaccines from excess heat, the better-known hazard, cold chain practices may risk exposing vaccines to freezing temperatures, which may also have an adverse effect on vaccine potency. Some of the most widely used vaccines are freeze-sensitive, including:
- Diphtheria
- Tetanus
- Pertussis
- Liquid Haemophilus influenzae type b (Hib)
- Hepatitis B
PATH Analysis
The hazards of accidental freezing of vaccines have prompted researchers to investigate and better characterize the risk. A 2007 literature review, conducted by PATH with support from the Bill & Melinda Gates Foundation, analyzed 35 studies and found that accidental freezing was pervasive and occurred across all segments of the cold chain.
PATH’s analysis revealed that, during transport, the occurrence of freezing temperature exposure was 16.7% in developed countries and 35.3% in developing countries. During storage, the occurrence of freezing temperature exposure was 13.5% in developed countries and 21.9% in developing countries. Notably, exposure to freezing temperatures occurred in both resource-rich and resource-limited settings, and the differences were not significant.
In the six studies analyzed by PATH that measured temperatures longitudinally through multiple sections of the cold chain, more than 75% of the vaccine shipments were exposed to freezing temperatures, indicating a potentially widespread failure to properly maintain the cold chain.
PATH Recommendations
Lacking thermostable vaccines that can be stored at ambient temperatures, PATH researchers offered several recommendations intended to minimize the potential for freeze damage.
These include using cool water packs instead of frozen ice packs during cold box transport (the World Health Organization recommends “conditioning” ice packs by allowing them to begin to melt before placing them in transport cold boxes), educating vaccine managers and handlers about freeze-sensitive vaccines, and providing clear vaccine handling procedures.
Improving the cold chain infrastructure by providing better refrigerators that limit the possibility of inadvertent vaccine freezing, and instituting electronic monitoring devices that signal exposure to an established temperature, may also lower the risk.
As an alternative to reliance on the cold chain, VBI’s LPV™ technology enables thermostable vaccine delivery, which is expected to increase vaccine safety, efficacy, and access in both established and emerging markets. Learn more about VBI’s thermostable vaccine technology >>
