Vaccines are sensitive to temperature excursions, but not as most people may think. A common assumption is that they must be kept cool and elevated temperatures are the problem. While it is true, increased temperatures will degrade the vaccine efficacy, it is much less damaging than freezing. Many drugs and vaccines have a “drug stability budget” which is the total allowable time the substance can be exposed to elevated temperatures during its lifetime. Elevated temperatures degrade the vaccine over time, and so you should not exceed this budget.
The major problem facing vaccine storage is actually freezing temperatures. A frozen vaccine is a dead vaccine. Some studies suggest that between 14-35% of refrigerators involved in the transportation and cold chain logistics expose vaccines to freezing temperatures. Further studies that looked at the complete end to end supply chain found that between 75-100% of vaccine shipments were exposed. As higher cost, freeze sensitive vaccines become more prevalent, it is becoming ever more critical that the world is receiving fully potent, non compromised vaccines.
Vaccines are a vital tool for public health. They save an estimated 3 million lives per year, and have helped eradicate diseases such as smallpox, and gone a long way to decreasing the world’s cases of tuberculosis and polio. It is therefore recognized as important to global health care that quality and effective vaccines are delivered. This can especially be a problem in rural areas of the world. So how can you ensure quality vaccines are delivered from the manufacturer to the vaccine recipient?
The World health organization and manufacturer guidelines recommend that all vaccines (except the oral polio vaccine) be kept between 2-8°C during distribution. If however the cold chain logistics and distribution system is not well versed in handling vaccines, a poorly functioning cold chain can deviate from this temperature. That means the vaccines can be exposed to a range of high or low temperatures. The damage from accidental freezing can result in lost potency. The most common freeze sensitive vaccines are those from tetanus, hepatitis B and Diphtheria. It is common for cold chain logistics to focus on protecting the vaccines from exposure to heat. This has resulted in the accidental freezing of vaccines being an overlooked problem, despite over 31% of vaccines distributed by Unicef in 2005 being freeze sensitive. That means UNICEF alone had an exposure of $439 Million USD in vaccines that could be damaged by accidental freezing.
A study published in vaccine in 2007 found that in developed countries the occurrence of vaccine freezing was around 16.7%, compared to 35.3% in developing countries. This showed that the current transport and cold chain logistics practices in all countries was problematic. Vaccines were usually placed in containers with frozen ice packs. Sometimes the WHO recommendations of conditioning the ice packs, allowing them to melt a little, before packing was not followed.
The study did not reach a conclusion as to the proportion of vaccines actually damaged by freezing temperatures, but it does recognize that there must be some effect as it is well known the potency of vaccines changes when freeze-sensitive vaccines undergo a change to a frozen state. It has also been pointed out by epidemiological studies that exposure of vaccines to freezing temperatures can be a contributor to the low immune response observed in vaccinated individuals.
By analysis of the available data, it is clear that the storage of vaccines at a stable and controlled environment with proper preventative measures for freezing is needed. In addition to educating the cold chain logistics handlers on the best practices for freeze-sensitive vaccines, the use of temperature data loggers and early warning IoT based systems can save millions in lost vaccines.