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Digital Data Loggers

Digital data loggers (DDLs), also called “continuous temperature monitoring devices” or just “data loggers,” continuously read and record temperatures to provide an accurate report of vaccine temperatures over time. DDLs also alert clinic staff when temperatures are out of the recommended range via visual, audible and/or electronic notifications. DDLs read and record temperatures at set time intervals and store data in an internal memory. Clinic staff can download and save the data as an electronic file on a computer and analyze vaccine storage unit temperature trends over time.

All VFC providers must use a VFC-compliant DDL in every refrigerator and freezer storing VFC-supplied vaccines. Practices also must have at least one battery operated backup DDL to use when a primary device is being calibrated, during emergency vaccine transport, or if a primary device fails.  Depending on the size of the practice, additional devices may be needed. Every device must have a valid and current certificate of calibration on file.  

Because monitoring devices experience a “drift” over time that affects their accuracy, DDLs must be certified for accuracy every two years, or three years when manufacturers recommend a period longer than two years. Calibrate primary and back-up devices on different schedules to ensure all refrigerators and freezers are always equipped with data loggers with a valid and current certificate of calibrations. VFC also encourages calendaring calibration testing so that it is done at least 2-3 months prior to a DDL’s expiration date. DDL expiration dates should be documented on the clinic’s Vaccine Management Plan.

In preparation for the annual VFC Program Recertification process, clinics are strongly encouraged to verify all their DDLs are calibrated and that the certificates of calibration are current.

Importance and Use of Data Loggers

Data loggers

  • monitor vaccine temperatures continuously—even when the practice is closed,
  • may have alert capabilities to notify clinic staff of temperature excursions during non-business hours,
  • determine how long vaccines have been exposed to out-of-range temperatures,
  • prevent unnecessary vaccine losses when excursion time frames cannot be precisely determined, and
  • show how a storage unit’s temperature increases and decreases over time.

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