Thermal Analysis of Refrigeration Systems Used for Vaccine Storage
Michal J. Chojnacky, Gregory F. Strouse
The CDC administers over $3 billion worth of vaccines per year through the Vaccines for Children program. Vaccine storage temperature is critical to maintaining drug potency, and as much as one-third of delivered vaccines are wasted due to thermal excursions. In this presentation, we present the findings from our study of various refrigeration units and temperature monitoring methods used in vaccine storage systems. For each model tested, multiple temperature sensors were arranged throughout the refrigerator space, providing a thermal map of the unit over time and across varying conditions. Three of the four refrigerator models tested successfully maintained vaccine vials within the specified 2 °C to 8 °C temperature range across the spectrum of tested conditions. However, we found that some storage methods and locations provided better temperature stability than others. The performance of the dorm-style refrigerator model suffered from significant temperature set point drift, large internal temperature gradients and overall instability. As a result, this model is not suitable for vaccine storage. Based on this study, we recommend that vaccine providers use some form of continuous temperature monitoring in their refrigeration units. Manual thermometer checks do not sufficiently capture temperature behavior over time, making it impossible to know whether thermal excursions might have occurred when no one was around to monitor the thermometers. The use of carefully placed electronic temperature loggers is a simple and inexpensive way to dramatically improve vaccine storage practices. By continuously monitoring vaccine temperature, providers can easily validate the efficacy of their vaccine supply, improve consumer confidence, and greatly reduce the incidence of waste.