Every vaccine storage unit must have a temperature monitoring device (TMD). CDC recommends that vaccines be monitored using a “digital data logger” (DDL). A DDL provides the most accurate storage unit temperature information, including a detailed record of how long a unit has been operating outside the recommended temperature range (referred to as a “temperature excursion”). Unlike a simple minimum/maximum thermometer, which only shows the coldest and warmest temperatures reached in a unit, a DDL provides a log of the temperature recorded at preset intervals (at least every 30 minutes is recommended).
Many DDLs use a buffered temperature probe, which is the most accurate way to measure actual vaccine temperatures. Temperatures measured by a buffered probe match vaccine temperatures more closely than those measured by standard thermometers, which tend to reflect only air temperature. Temperature data from a DDL can either be downloaded to a computer using special software or retrieved from a website. The software or website may also allow you to set the frequency of temperature readings. Reviewing DDL data regularly is critical to ensure temperature excursions that could damage vaccines do not go on without being addressed. It is important to decide whether independent software or a website program works best for your facility.
Temperature monitoring devices that are NOT recommended include alcohol or mercury thermometers, even if placed in a fluid-filled, biosafe, liquid vial; bimetal stem devices; devices used for food; chart recorders; infrared devices; and devices that do not have a current and valid Certificate of Calibration Testing. Please note that some devices sold in hardware and appliance stores are designed to monitor temperatures for household food storage. They are not calibrated and not accurate enough to ensure vaccines are stored within the correct temperature range. Using these devices can pose a significant risk of damaging vaccines due to undetected out-of-range temperatures.
More details on temperature monitoring are available on pages 10–11 of CDC Vaccine Storage and Handling Toolkit, available at www.cdc.gov/vaccines/hcp/admin/storage/toolkit/storage-handling-toolkit.pdf. Additional details about temperature monitoring for COVID-19 and mpox vaccines are available in the addendum at the end of the toolkit.