Calibration stability of data loggers used for vaccine temperature monitoring

Abstract

Continuous temperature monitoring of vaccines during distribution and storage is critical to ensuring vaccination efficacy. Exposure to inappropriate storage temperatures can degrade vaccine potency, putting products and patients at risk if excursions go undetected. Digital temperature data loggers are widely used by U.S. vaccine providers to maintain a continuous record of vaccine storage temperature history. However, whether specific handling or usage conditions contribute to measurement drift in data loggers is not well known. Here we show that data logger calibration status is largely unaffected by typical usage conditions encountered at the vaccine provider level. Forty commercial digital data logger devices representing eight unique models marketed for use in vaccine temperature monitoring were evaluated in a two-year period during 2019-2021. The devices were calibrated upon receipt, subjected to trials designed to simulate typical usage conditions, and then recalibrated periodically to evaluate potential measurement drift. Simulated usage conditions included daily use in vaccine refrigerators and freezers, battery changes, local transport, cross-country shipment, and long-term storage. Out-of-tolerance calibration measurements were extremely rare, and the few failures we detected did not appear to be correlated with any of the usage trials performed during the two-year study period. These findings support extending data logger recalibration intervals when paired with concurrent manufacturer-supplied device stability data and/or intermediate data logger verification checks performed in the field.