Straight to the Point

It is critical for facilities that manufacture, handle, or store vaccines to have a properly functioning and reliable environmental monitoring system. Accurate readings of refrigerator and freezer temperatures may prevent vaccines from being compromised. When a vaccine’s integrity is questionable, it’s possible that the efficacy or potency of the vaccine diminishes. This can result in a loss of time, money, and resources. More importantly, a brand’s reputation may be diminished if the vaccine is ineffective or the patient suffers an unexpected consequence.

There is, however, a way to reduce the risk that a vaccine is destroyed during storage. The solution to become aware of this potential situation is to install a reliable environmental monitoring system. When it comes to choosing the right system, there are many factors to consider. The Center for Disease Control and Prevention has provided guidelines for temperature monitoring equipment.

According to the guidelines, all of the following equipment is recommended to fully ensure the safety of a vaccine being stored.

  • Stand-alone refrigerator(s) or freezer(s) with enough space to accommodate your maximum inventory without crowding. The refrigerator should maintain temperatures between 2°C and 8°C (36°F and 46°F); freezers between -50°C and -15°C (-58°F and +5°F).


  • Digital data logger with a current and valid Certificate of Calibration Testing (Report of Calibration) for each unit.


  • At least one backup monitoring device in case of a broken or malfunctioning logger.  Backup should also have a current and valid Certificate of Calibration Testing.


  • Digital Display easily readable from outside the unit with current, minimum and maximum temperature readings displayed (accuracy within +/- 1°F or +/- 0.5°C).


  • Detachable probe in a buffered material that should closely reflect vaccine temperatures rather than air temperatures. Glycol, glass beads, sand, or TeflonⓇ are noted as example buffer materials.


  • Alarm for out-of-range temperatures.


  • Low battery indicator.


  • Memory that stores at least 4000 readings


  • User programmable logging interval (or data logger sampling rate) no less frequently than every 30 minutes.


  • Diagrams or technical drawings of the facility showing the layout of critical components

When digital data loggers are used to monitor a vaccine’s environment, it is critical that they have been calibrated and that the calibration has been documented. The CDC recommends that users are in possession of a current and valid Certificate of Calibration for each data logger. A certificate should contain critical information such as: model or device name/number, serial number, calibration date, confirmation that the instrument has passed testing, and a margin of error of less than +/- 0.5 °C.

Where should you monitor temperature within a refrigerator?

Correct placement of a temperature sensor is key to accurately monitoring your vaccines. Refrigerators are not all built equally and their dimensions are often different from one another. Not only are there spatial considerations to be aware of when placing sensors, but there are also other factors to be aware of such as the refrigeration cycle, air circulation patterns, use patterns (frequency of opening and closing the door, temperature set point, etc.), and environmental conditions.

Vaccines can be stored anywhere inside a ‘purpose-built’ or ‘pharmaceutical grade’ refrigerator because they are capable of keeping uniform temperature throughout and the ability to recover temperature quickly. If using a household grade or a combination refrigerator/freezer unit follow the CDC guidelines for vaccine storage which state: vaccines should never be on a top or bottom shelf, rather, inventory should be well labeled and placed on center shelves with space between closed boxes. This helps ensure good air circulation and a more consistent temperature. By placing the temperature sensor among the vaccines themselves, it becomes subject to the same temperature fluctuations and air flow patterns that the vaccines experience. Implementing a temperature sensor with a buffer solution that has the same thermal conductivity as the vaccine allows it to closely imitate a vaccine’s fluctuating temperature (buffer heats up or cools down at the same rate as a vaccine).

Locations within the refrigerator that are most susceptible to fluctuations in temperature, near the door, for example, provide the most unstable conditions. Placing additional sensors in these locations will not replicate a vaccine’s temperature, but can demonstrate the worst-case scenario. You can claim that no location in the refrigerator was warmer than the temperature at that particular point.

Data Logger Installation

It is recommended that data loggers be installed outside of refrigerators in an easily visible area, preferably on the side nearest the door hinge. The sensor and cables stemming from the data logger should enter the refrigerator through the hinge. Once inside, securing the probe onto the fridge can easily be done with cable tie mounts and zip ties. Thread the cable through the mounts along the edges of the refrigerator. All cables should be fastened along the edge of the refrigerator so they are out of the way, removing any possibility of spills caused by snagging the wires while working inside the refrigerator. The bottle that contains the buffer and sensor should be placed in a holder and fastened down to prevent accidental movement. Keep the sensor within close proximity to the vaccines to best represent the conditions of your assets.  

If a glycol buffer is used to dampen temperature fluctuations around the sensor, check to ensure that the glycol level in the vial is high enough to submerge the sensor completely. Depending on the installation process, it is not uncommon for glycol to leak or spill. Performing this check is a simple task that may prevent complicated issues from occurring in the future.

Have a conversation with the Experts

There are many other factors to take into consideration when implementing a vaccine refrigerator in conjunction with an environmental monitoring system. Setting up a properly operating refrigerator and monitoring system that will satisfy CDC and FDA auditors can be quite the challenge if your team is unpracticed in installations. Following the guidelines laid out above and reading up on documentation provided by regulatory bodies can help you ensure that you’re maintaining industry compliance.



1.CDC Vaccine Storage and Handling

2.Vaccine Storage and Handling Toolkit

3.NIST: Guideline for Storage and Temperature  Monitoring of Refrigerated Vaccines