Methods for Accurate Cold-Chain Temperature Monitoring Using Digital Data-Logger Thermometers

Background: The CDC administers over $3 billion worth of vaccines per year through the VFC program. Accurate, continuous temperature monitoring is critical to determining whether drug potency has been maintained throughout shipment and storage, yet is not  practiced at all levels of the vaccine cold chain. VFC providers are not required to use continuous temperature monitoring systems in their vaccine refrigerators. Thermometers may be used incorrectly, or may not meet accuracy requirements. Vaccine providers may purchase thermometers because they are listed as certified or NIST traceable, yet the veracity of these statements often lacks official status, authentication and/or validation.

Objectives: We have tested the performance of multiple temperature monitoring systems for use in both shipping and refrigerated storage of vaccines, including both chemically-activated sensors and digital data-logger thermometers. All of the tested devices will be evaluated for accuracy, proper methods for use, and usefulness in continuous temperature monitoring. These results will be used to develop specifications and protocols for NSF certification of cold chain thermometers.   

Methods: Eight digital data-logger thermometers were tested under varying conditions in five different vaccine refrigerator models to:

• Evaluate manufacturer stated accuracy over the range of 0 °C to 10 °C
• Quantify stability over six months
• Determine their proper use within a vaccine storage system so that temperature measurements reflect vaccine vial temperatures.

The performance of chemically-activated and digital electronic data-loggers engineered for monitoring vaccine shipments was tested in a laboratory setting and under shipments to both warm and cold locations.

Results: Properly located, data-loggers accurately monitored vial temperatures for extended periods of time.

Conclusions: Widespread use of continuous temperature monitoring at all levels of the cold chain will greatly improve confidence in the efficacy of delivered vaccines. Digital data-loggers offer an affordable and practical means for effective cold chain temperature monitoring.