FRESH: Vaccine Refrigeration for Developing Regions

For more information, read our proposal or view our proposal defense presentation

Our background research is divided into two major sections; The first section was the cold chain, which the global system of cold rooms, refrigerators and cold transport that allows vaccines and other perishables to be distributed. We are looking into both its abilities and inadequacies. The second part of our background research was into various methods of refrigeration.
As of now, we are focused on vapour-compression refrigeration and phase change materials.

Cold Chain
Phase Change Materials

The steps of the cold chain

The vaccine delivery system, called the cold chain, starts with large shipments of up to 1.5 million vials of vaccines that are shipped or flown, in refrigerated containers or compartments, from the manufacturer to the Ministry of Health of the country that placed the order. The vaccines are stored in a cold room at the airport until a refrigerated truck delivers them to the Ministry of Public Health, or a primary vaccine store. Vaccines are delivered quarterly from the Ministry of Health to regional centers, and from there are delivered monthly to provincial health centers. From the provincial health centers, vaccines are delivered as needed to local health centers and outreach clinics. Refrigerated trucks are used in areas with large regional populations; while elsewhere the entire system is comprised of cold boxes, which will not be able to meet the estimated volume of vaccines. The entire delivery process, depending on demand, ranges from one to three months.

Problems in the cold chain result directly in the decreased potency of vaccines. It is estimated that because of problems in the cold chain 70% of vaccines are rendered impotent. This results from freezing during transportation, unreliable energy at local level facilities, and a dearth of long-term storage at local facilities. Due to these holes in the cold chain, current immunization programs such as the World Health Organization's Extended Programs on Immunization are not as efficient as they could be.

Phase change materials (PCMs) are materials that have a high heat of fusion (energy per unit mass to change from solid to liquid). This feature allows them to store a great amount of energy at a constant temperature by absorbing the heat entering the

refrigeration system, which slows temperature change. PCM technology also does not require a constant energy source because it uses the change in a substance's phase to store and release energy. PCM technology has the potential to be integrated with other technologies into existing systems. For example, a PCM can be added to a compression refrigerator and used to minimize temperature fluctuations. This would enable maintenance of the necessary 2-8 ° C temperature range and prevent temperature swings caused by refrigerators with inefficient feedback and control systems.

A good example of a PCM is ice water. Any energy entering the system will melt the ice, without raising the temperature of the drink. Technically, using ice packs for refrigeration is using phase change materials, but ice packs often freeze the vaccines, so this study is focused on PCMs with melting points from 2-8 ° C.