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National Vaccine Storage and Handling Guidelines for Immunization Providers (2007)
Section 3 Vaccine Storage Equipment
Contents
3.1 General Requirements
3.2 Back up Equipment
3.3 Routine Equipment Maintenance Logbooks
3.4 Refrigerators and Freezers
3.5 Refrigerators and Freezer Maintenance
3.6 Thermometers and Temperature Monitors
3.7 Thermometer Maintenance
3.8 Cold Chain Monitors
3.9 Vaccine Security
3.10 References
3.1 General Requirements
Vaccine storage units must be selected carefully and used properly. Any refrigerator or freezer used for vaccine storage must
- Be able to maintain required vaccine storage temperatures through all seasons.
- Be large enough to hold the year's highest monthly inventory, including influenza season.
- Have a calibrated thermometer or data logger inside each storage compartment.
- Be dedicated to the storage of vaccines only.
- Be placed in a secure location away from unauthorized and public access.
3.2 Backup Equipment
No piece of vaccine storage equipment is infallible. At some point, equipment failure will occur because of a power failure, breakdown, or normal wear and tear. Vaccine security requires that these failures be anticipated and that backup equipment and backup plans be available. Regular maintenance of all equipment is recommended to maintain optimal functioning.
3.3 Routine Equipment Maintenance Logbooks
An equipment logbook should contain the following records of each piece of equipment:
- Date of installment
- Equipment instructions and list of routine maintenance tasks
- Dates of any routine tasks performed (e.g. cleaning)
- Dates of repairs or servicing
- The name of the person, company and contact information (operational and after hours) of the company providing service
3.4 Refrigerators and Freezers
Technical Requirements
There are many different types of refrigerator and freezers available. Knowing the functions and components of the refrigerators will help in understanding why certain types of refrigerators and freezers are recommended for vaccine storage. The technical features of refrigerators that can affect the safe storage of vaccines are outlined below(1).
1) Temperature regulation
The compressor functions to cool the inside of the refrigerator. The compressor is controlled by either a thermostat or a digital controller, depending on the type of fridge. When the temperature exceeds the set temperature of the thermostat, the compressor turns on and operates to cool the fridge. The point at which the compressor turns on depends on the design of the thermostat and fridge. Therefore, a thermostat that has a large differential between its switch points (on and off) will cause, in turn, long compressor on and off periods. This may produce large temperature fluctuations that are undesirable for the storage of vaccines.
2) Defrost mechanism
The cooling area in the refrigerator is called the evaporator. It consists of cooling coils usually located behind the surface of the wall, at the back of the refrigerator or in the exposed area at the back of the refrigerator. Heat from the warm air inside the fridge transfers to the refrigerant in the coils. As warm air passes over the evaporator, water vapor in the air condenses and freezes on the evaporator. During the process of cooling the refrigerator, an icy build up is created on the evaporator. The ice that forms may reduce the cooling capacity and efficiency of the system. Therefore, refrigerators must have a defrost cycle that allows the ice to melt off the evaporator. Ideally, the temperature remains at the set point (within the range of +2°C to +8°C) during the defrost cycle.
3) Spatial temperature differential
Spatial temperature differentials are the differences in temperatures within the fridge. Vaccine storage requires a uniform temperature distribution to prevent placement of vaccines outside the recommended temperature ranges.
4) Effects of changes in ambient temperature
Ambient temperature is the temperature of the environment where the fridge is kept. The aim is to have a refrigerator that can maintain a stable temperature within, even when the surrounding temperatures change.
5) Temperature recovery
Temperature recovery is the ability of the refrigerator to return to its set temperature after being exposed to elevated temperatures (e.g. after opening the door to remove vaccine).
Knowing the functions and components of different storage units will help understand why only certain units are recommended for vaccine storage.
Purpose-Built Refrigerator
A purpose-built vaccine refrigerator (also referred to as a pharmacy, lab-style or laboratory grade refrigerator) is the standard for storing large inventories of vaccines for several reasons. See Figure 1 for a picture of an example of a purpose-built vaccine refrigerator. The advantages of a purpose-built refrigerator, in terms of the technical features, are outlined below(1).
1) Temperature regulation
The temperature regulation mechanism in a purpose-built vaccine refrigerator has a very tight temperature tolerance and a quick reaction time to temperatures outside of the set range. A temperature probe for the temperature control is usually located in the path of the return airflow, thereby measuring the temperature of the warmest air in the refrigerator.
2) Defrost mechanism
Purpose-built vaccine refrigerators have a mechanism to defrost ice from the evaporator without raising the temperature in the unit. There is a small heating element wrapped around the evaporator coils that has the capacity to melt the frost off the evaporator frequently. This feature prevents the lengthy periods of time needed for defrosting in other refrigerator designs. This method of regular defrosting also prevents fluctuations of temperatures within the unit.
3) Spatial temperature differential
The spatial temperatures are tightly controlled in purpose-built vaccine refrigerators. There is constant fan-forced air circulation within the refrigerated compartments. Generally, the temperature does not vary within the storage area from the set point.
4) Effects of changes in ambient temperature
The forced air circulation helps to keep internal temperatures within a range even when the ambient temperature changes.
5) Temperature recovery
The temperature is digitally managed in purpose-built refrigerators. Any deviation in temperatures from the pre-set one is sensed very rapidly.
Note: As a result of the glass door design of the purpose built refrigerators, extra effort must be taken to protect vaccines from light exposure at all times. It is important to be aware that one limitation of purpose built refrigerators is that glass doors do not provide good insulation in the event of a power interruption, resulting in a rapid rise in temperature.
Advantages of a purpose-built vaccine refrigerator(1)
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Figure 1: Purpose-Built Vaccine Refrigerator Features
Domestic Frost-Free Versus Manual and Cyclic Defrost Refrigerators
A domestic combination refrigerator and freezer unit is acceptable, but requires significant modifications to store vaccines. The refrigerator and freezer compartments must have separate external doors and the unit must meet the criteria set out in these guidelines. There are two types of domestic refrigerators: domestic frost-free, and manual and cyclic defrost. Figures 2 and 3 illustrate examples of a domestic frost-free refrigerator and a manual and cyclic defrost refrigerator, respectively.
Domestic frost-free refrigerators refer to the freezer compartment where food is supposed to stay relatively frost-free. The evaporator is located in the freezer (usually behind the rear wall). The evaporator defrosts automatically with a heater that dissipates the defrost water. When the compressor is on, a fan blows the cool air through vents to the freezer and then to the refrigerator. Thus, the air being circulated to the refrigerator may be below 0°C. The cool air may damage vaccines if they are placed near the vents. Depending on the refrigerator model, some frost-free refrigerators may provide more uniform temperatures than manual and cyclic defrost models and may be more suitable for vaccine storage.
Figure 2: Domestic Frost-Free Refrigerator
Manual and cyclic defrost refrigerators refer to the refrigerator. The evaporator in the refrigerator automatically defrosts whereas the freezer needs to be manually defrosted. The evaporator is most commonly found as an exposed vertical plate at the back of the refrigerator. Manual and cyclic defrost refrigerators have not been recommended for vaccine storage because of the significant temperature variations and the risk of vaccines freezing. Generally, while the compressor is running, the area near the evaporator can be very cold whereas other areas are much warmer.
Figure 3: Manual and Cyclic Defrost Refrigerator
Domestic refrigerators are designed for food storage and not for the requirements of vaccine storage. Precautions and fridge modifications are needed in order to store vaccines.
Technical Information for Domestic Refrigerators
The technical features of domestic refrigerators that can affect vaccine storage are outlined below.(1).
1) Temperature regulation
The thermostat in domestic refrigerators detects temperature changes and controls the compressor's on and off function. When the temperature exceeds the set temperature of the thermostat, the thermostat sends a signal to the compressor to cool the unit. Large fluctuations in temperatures may occur depending on the point at which the compressor turns on and the time it takes to cool the unit. This will vary depending on the specifications of the refrigerator.
Domestic refrigerators are designed to cool the unit by air blown at below 0°C from the evaporator into the refrigerator. Products placed close to vents will experience these below 0°C temperatures.
Finally, temperature sensors are located in various areas of the refrigerator depending on the model. The sensors may not measure the temperature where the vaccines are stored, thereby possibly exposing vaccines to temperatures outside the recommended range when the evaporator blows cold air into the refrigerator.
2) Defrost mechanism
Depending on the type of domestic refrigerator, there are two main mechanisms for defrosting. A frost-free refrigerator relies on heating coils wrapped around the evaporator in the freezer. The heating coil is controlled by a timer and/or a sensor that determines when a predetermined temperature is reached and when the heating coil should be turned off. There is a risk of temperature fluctuations that may result in higher temperatures in the freezer and sections of the refrigerator.
In a manual and cyclic defrost refrigerator, the freezer defrosts manually and the refrigerator relies on natural melting or off-cycle heating of the evaporator when the compressor is off.
The defrost mechanism in domestic refrigerators can cause temperature fluctuations within the unit. The combination of the compressor cooler, the defrost heating, as well as poor uniformity of temperatures throughout the compartments, creates temperature variations which can affect vaccine storage.
3) Spatial temperature differential
Domestic refrigerators are designed to have various temperature zones for multiple storage functions. They are designed so that there is transfer of cool air from the freezer to the refrigerator. In turn, this could result in vaccines being stored in suboptimal conditions.
4) Effects of changes in ambient temperature
In domestic refrigerators, the temperature sensor may be located in the freezer. As a result, when the ambient temperature rises, the compressor operates more frequently, and the refrigerator gets exposed to cooler air from the evaporator.
5) Temperature recovery
In domestic refrigerators, temperature recovery depends on many factors including the design of the refrigerant delivery system and temperature regulation system; the size of the compressor, evaporator and fan; and the time it takes for the temperature sensor to detect a change in temperature.
General information about a domestic refrigerator includes:
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The vaccine coordinator must know the following information about their refrigerator if a domestic refrigerator is going to be used to store vaccines:
(See Know your Refrigerator in Section 4—Vaccine Storage Practices.) |
Bar Fridge Units
Any style of small single-door (bar-style) fridge is unpredictable in terms of maintaining temperatures and should not be used. With combined refrigerator and freezer units, the freezer compartment in this type of unit is incapable of maintaining temperatures cold enough to store freezer-stable vaccines. Even when the freezer temperature is not adjusted, the temperature in the refrigerator compartment will fall below the recommended range, potentially freezing the refrigerated vaccines. Temperatures vary inside the compartment. The temperature-control sensor reacts to the temperature of the evaporator rather than to that of the air in the compartment, resulting in varying temperatures in the refrigerator as the ambient temperature changes(1).
Jurisdictions in Canada report that use of bar fridges for vaccine storage is a leading cause of cold chain breaks.
Any style of small single-door (bar-style) fridge is unpredictable in maintaining temperatures and is not recommended for vaccine storage. Jurisdictions in Canada report that use of bar fridges for vaccine storage is a leading cause of cold chain breaks.
Equipment Placement
Good air circulation around the vaccine storage unit is essential for proper heat exchange and cooling functions. The unit should be placed in a well-ventilated room and should have space around the sides, top and back. Leave at least 10 cm of space (or as recommended by the manufacturer) between the back of the unit and the wall. If the unit has coils on the back, measure 10 cm from the coils to the wall. Nothing should be blocking the cover of the motor compartment, which is normally located at the back or the side of the unit. Make sure that the unit stands firmly and level, and that the wheels or leveling legs are adjusted so that the bottom of the unit sits 2.5 to 5 cm above the floor. Do not place in direct sunlight, near a heat source, or along an outside wall where the temperature of the wall can vary, depending on the season(2).
Recommended Temperature Range
Refrigerator
The refrigerator compartment should maintain temperatures between +2°C and +8°C. The temperature should never fall below +2°C or rise above +8°C. Therefore, set the temperature mid-range to achieve an average of about +5°C. This temperature setting will provide the best safety margin of temperature fluctuations within the +2°C to +8°C range.
Freezer
Vaccines that must be frozen should be maintained at a temperature of -15°C or colder.
Setting and Stabilizing the Temperature
Who should adjust the temperature?
Only the designated vaccine coordinators should adjust the temperature of a vaccine storage unit. Limiting access to the thermostat reduces the risk that the temperatures will be adjusted inappropriately. If the thermostat requires adjustment, alert the designated vaccine coordinator.
A warning sign should be posted on the storage unit that says, “Do not adjust refrigerator or freezer temperature controls. Notify primary vaccine coordinator or the back-up coordinator if adjustments are necessary.”
Thermostats
Refrigerator and freezer thermostats are marked in various ways, depending on the brand. In general, thermostats do not show temperatures but rather the levels of coldness. For example, some have a series of numbers or letters on the control knob. Others may have “MIN,” “MED,” and “MAX” marked on the knob. The only way to know the temperature inside the unit is to measure it with a thermometer. In combination refrigerator and freezer units, the thermostat actually controls the volume of cold freezer-temperature air that goes into the refrigerator. Consult the manufacturer's guidelines for instructions on how to operate the thermostat.
Only the vaccine coordinators should adjust the temperature of a vaccine storage unit.
How to adjust the temperature
To adjust the temperature:
- Be sure the unit is plugged into the power source.
- If necessary remove all vaccines and store appropriately.
- Check the temperatures inside the refrigerator and freezer compartments.
- Adjust the temperature indicator slightly toward a warmer or colder setting as necessary. Adjust the thermostat slowly so as not to exceed the recommended temperature range.
- Allow the temperature inside the unit to stabilize for half an hour then recheck the temperature. Adjust the thermostat again as necessary. If the refrigerator is newly installed or newly repaired it should be preconditioned to the set point temperature and stabilized. Allow one week of twice daily refrigerator and freezer temperature recordings before using the unit to store vaccines.
- Always strive for +5°C to stabilize the refrigerator temperature. Make sure the temperature does not fall below the lower limit or rise above the upper limit of the recommended refrigerator temperature range of +2°C to +8°C.
- Aim to stabilize the freezer temperature at -15°C or colder.
- Be sure the temperature in the refrigerator has stabilized before returning vaccines that have been removed.
Combined refrigerator and freezer units use a cooling system that directs cold air from the freezer compartment into the main refrigerator compartment. Therefore, be careful when adjusting the freezer temperature because this will affect the temperature of the air venting into the refrigerator compartment. Without careful and frequent temperature monitoring inside the refrigerator compartment, there is a danger of freezing the refrigerated vaccines.
Frequent temperature monitoring of both the freezer and refrigerator compartments throughout the day, as well as at the beginning and end of the workday, is required whenever thermostats are adjusted. The temperature in a newly installed or newly repaired refrigerator may take 2 to 7 days to stabilize within the recommended range of +2°C to +8°C. The temperature in a newly installed or newly repaired freezer unit may take 2 to 3 days to stabilize within the recommended range of -15°C or colder. Allow one week of twice daily refrigerator and freezer temperature recordings before using the unit to store vaccines.
Consider re-loading the refrigerator with vaccines at the beginning of a work week. Monitor newly adjusted fridge temperatures closely after loading with vaccines. The presence of vaccines has a major impact on the temperature of the refrigerator, especially when using domestic models(3).
To maintain the cold chain during any period when the refrigerator or freezer is out of service, vaccines should be temporarily stored in a temperature monitored alternate vaccine storage unit until the temperature in the original unit can be stabilized within the recommended range. Another option is to store the vaccines in an appropriately packed cooler if the storage unit will be out of service for a short time and vaccine-appropriate temperatures can be maintained in the cooler for the time required. (See Section 9— Vaccine Shipments for more details.)
Allow 1 week of twice daily refrigerator and freezer temperature recordings before using a newly installed or newly repaired refrigeration unit to store vaccines.
Factors Affecting Temperature Variations
Temperatures can vary in a vaccine storage unit based on the contents/load, seasonal temperature variation, how often the door is opened and power interruptions. The only way to be sure the temperature in the storage unit has remained within the recommended range is to frequently monitor and record the temperature using a min/max thermometer or data logger. (See Know Your Refrigerator in Section 4—Vaccine Storage Practices for more details.)
Opening the door
Limit the number of times the vaccine storage unit doors are opened and avoid letting the doors stand open unnecessarily. Not only does this affect the temperature in the unit, it also exposes the vaccines to light (which can affect the potency of some vaccines). Routinely check the doors throughout the day and at the end of the day to ensure they are tightly closed.
Avoid unnecessarily opening the refrigerator door. The World Health Organization recommends door openings be minimized to not more than four times a day.
Stabilizing the temperature with water bottles and frozen packs
You can help stabilize the temperature in the refrigerator by keeping two or more large containers of water inside. Store the water bottles in the crisper area, in the door racks, and/or against the inside walls of the refrigerator. You can help stabilize the temperature in the freezer by keeping frozen packs or ice trays inside. Store the frozen packs along the walls, back, and bottom of the freezer compartment and inside the racks of the freezer door. Not only will water bottles and frozen packs help maintain an even temperature in the compartments with opening and closing of the doors, they will also help keep the temperatures stable longer in the event of a power failure.
Vegetable bins (“crispers”)
Consider removing the vegetable bins from the refrigerator. Removing the bins not only provides extra space for storing containers of water, but it also removes the temptation to use the bins for storage of food, beverages, or vaccines. Vaccines should never be stored near the floor of the refrigerator in the vegetable bins because the temperature in this area is different from that in the body of the refrigerator. (See Know Your Refrigerator in Section 4—Vaccine Storage Practices for more details.)
When to Adjust the Temperature
The refrigerator and freezer temperatures should be adjusted if outside the recommended range or if, over time, the temperature appears to be moving toward the upper or lower temperature limit. (See Section 6—Storage Troubleshooting for more details.)
In some situations, the thermostat may need to be reset in summer and winter, depending on the ambient temperature.
3.5 Refrigerators and Freezer Maintenance
General Principles
Regular maintenance is required to ensure proper operation, to maintain required temperatures, and to extend the useful life of the appliance.
The most important action to take if the vaccine storage unit is not working properly is to protect the vaccine supply. Move the vaccine to a properly functioning storage unit with appropriate temperatures. After this is accomplished, attempt to find the cause of the problem and correct it. (See Section 6—Storage Troubleshooting for more details.)
The most important action to take if the vaccine storage unit is not working properly is to protect the vaccine supply.
Daily Maintenance Tasks
Check the internal temperature
The minimum and maximum temperature inside each compartment of the vaccine storage unit must be checked with a calibrated thermometer and recorded numerically on a temperature log at least twice each day: once in the morning when the door is first opened and once at the end of the clinic day just before the door is closed for the last time. (See Section 5—Temperature Monitoring and use the Temperature Log for Vaccines (Celsius) in the Resources Section.) More frequent temperature monitoring is required following thermostat adjustments. The temperatures should be recorded on a temperature log and charted on a graph for visual focus when it is outside the optimal temperature range. If the temperature is outside the recommended range, the designated vaccine coordinator should be notified without delay. Immediate action must be taken. (See Steps in Handling Inappropriate Vaccine Storage Conditions (Light and Temperature) in Section 6—Storage Troubleshooting for more details.)
The temperature inside each compartment of the vaccine storage unit must be checked with a calibrated thermometer at least twice each day.
Check that the doors are closed
To maintain internal temperatures within the recommended ranges, the vaccine storage unit doors must fit securely and tightly against the unit. The rubber-like seals that run around the inner edges of the doors contain magnets that help hold the doors closed and create tight seals, keeping cold air inside. Check that the doors are properly sealed by giving a gentle tug on the door handles. The doors should also be checked at the end of each clinic day to make sure that they are properly closed and sealed. Installing an inexpensive Velcro™ latch from a hardware store can help ensure that the door is not accidentally left ajar.
Check that doors are properly sealed each time they are closed and at the end of each day.
Weekly Maintenance
Check ice buildup in the freezer (manual and cyclic defrost units only)
If you have a manual defrost freezer, it is quite normal for ice and frost to accumulate inside the compartment. A thin layer of frost does not affect the cooling performance but a thick layer of frost negatively affects the efficiency of the system.
Check the inside walls of the freezer compartment weekly. When frost has accumulated to a thickness of 1cm or so, the unit requires defrosting. Follow the manufacturer's guidelines for specific recommendations for defrosting the freezer.
General guidelines for defrosting a manual and cyclic defrost refrigerator include:
- Remove all vaccines from both compartments of the unit and place them into alternate storage unit(s) in accordance with written protocols.
- Turn off the power and unplug the unit.
- Remove all frozen packs from the freezer (keep frozen, if possible).
- Keeping the freezer door open, allow all the frost to melt.
- Loose ice can be removed by hand; no sharp tools or sharp instruments should be used to remove the ice.
- A container of warm water (not greater than +50°C) inside the compartment can reduce defrosting time.
- Once the frost has melted completely, clean thoroughly and wipe the unit dry. (This is also a good time to clean the refrigerator compartment.)
- Connect the power and ensure that the thermostat is turned to an appropriately cold setting.
- Wait for each compartment of the unit to stabilize at the proper temperature range.
- Monitor and record the temperature every half-hour for the next few hours.
- Re-stock each compartment with vaccine.
- Continue to monitor and record the temperature every half-hour for the next few hours.
If defrosting is necessary once a month or more frequently, the door may not be sealing properly, the door may have been opened too frequently, or there may be other mechanical problems with the freezer. (See Refrigerator and Freezer Door Problems in Section 6—Storage Troubleshooting for more details.) Consult a technician and monitor temperatures carefully.
Frost-free freezers do not need to be manually defrosted. They have regular defrost cycles three or four times a day when the freezer temperature increases and melts the ice automatically.
Quarterly Maintenance
Clean the coils and motor
The vaccine storage unit coils should be examined and cleaned quarterly. Dust and dirt build up affects the transfer of heat from the coils and, therefore, the efficiency of the unit. Unplug the unit and use a soft brush, cloth, or vacuum cleaner with an attachment hose to remove any dirt or dust from the surface of the coils. After cleaning, plug in the unit and document that the power is restored and that the temperature has been maintained. Avoid cleaning the coils and motor at the end of a Friday. Accidentally damaging the coils will cause a problem that may not be detected until the following Monday.
This process should only take a few minutes; therefore, it is not necessary to transfer the vaccine to another storage unit as long as the doors remain tightly closed for the duration of the procedure.
Clean the refrigerator and freezer compartments
Clean the refrigerator and freezer compartments quarterly or as needed. Remove the vaccines from the compartments and store them in a functioning unit. Unplug the unit or turn off the power and wash all inside surfaces and shelves with warm, slightly soapy water. Dry thoroughly then plug in the unit or turn the thermostat back to an appropriately cold setting. Wait for the unit to reach and stabilize at the proper temperature range monitoring and recording the temperature every half-hour for the next few hours. Restock each compartment with vaccine, continuing to monitor and record the temperature every half-hour for the next few hours.
Check the door seals
Quarterly, check the integrity of the rubber-like door seals. They should not be torn or brittle and there should be no gaps between the seals and the body of the unit when the doors are closed. The doors should open and close properly and fit squarely against the body of the refrigerator. For this to happen, the hinges must be correctly adjusted. If there are any problems with the door seals, consult a technician as necessary and monitor temperatures carefully. (See Refrigerator and Freezer Door Problems in Section 6—Storage Troubleshooting for more details.)
Use the Monthly Vaccine Inventory and Refrigerator and Thermometer Maintenance in the Resources Section as a summary of maintenance completed.
3.6 Thermometers and Temperature Monitors
All thermometers are calibrated (given a temperature scale) during manufacturing. Not all models of minimum and maximum (min/max) thermometers are calibrated with the same scale and may have different accuracies and resolutions. Please check with the manufacturer for the accuracy of your thermometer.
Calibration should be accurate within ±1°C. Avoid using thermometers that have not been calibrated to be accurate within ±1°C. (See “Thermometer Maintenance” later in this section for more details.)
Always use a thermometer that has been calibrated within ±1°C.
Types of Temperature Monitoring Devices
Overview
Immunization providers must be familiar with their jurisdiction's requirements for temperature monitoring equipment.
The only thermometers and temperature recording devices recommended for monitoring the temperatures within vaccine storage units are thermometers that provide continuous recording or min/max thermometers that are properly monitored. These types of thermometers are preferred because they provide an indication of the length of time a storage compartment has been operating outside recommended temperature ranges when a cold chain break occurs. The min/max thermometer must be reset regularly (after properly recording temperatures) for meaningful readings.
The only thermometers and temperature recording devices recommended for monitoring the temperatures within vaccine storage units are thermometers that provide continuous recording or min/max thermometers that are properly monitored.
1) Data Loggers
Digital data loggers are miniature, battery-powered, stand-alone temperature monitors that record hundreds or thousands of temperature readings. These are the ideal temperature monitors because they can indicate when the exposure occurred and how long the vaccines were exposed to the min/max temperatures. Data loggers may be single use and used only in transport, or they may be multiple use. Single-use data loggers have external lights (or symbols) that alert the user to out-of-range temperature events; a green light indicates the cold chain was properly maintained and a red light indicates inappropriate temperature exposure occurred. If a red light is seen, the vaccine shipment must await approval for use, and the device must be sent back to the manufacturer to interpret the temperature data.
Multiple-use digital data loggers are accompanied by special software that is installed in a computer. This software allows the user to set the frequency of the temperature readings, download data from the device, and calculate temperature averages, minimums, and maximums, as well as the time spent at each temperature. Data loggers should be replaced or re-calibrated annually.
Document the temperatures twice a day. Monitor for visual alarm whenever going into the fridge. Download data each morning because the data logger will detect any out of range temperature overnight.
2) Strip monitors
Strip monitors are battery-powered single-use units that record continuous temperature readings on a paper strip and may be used to monitor vaccine temperatures during transport.
3) Chart recorders
Chart recorders consist of a graph wheel with replaceable graph paper and ink pens. The pens mark the temperature on the graph paper as the wheel turns. Temperatures are recorded continuously, 24 hours a day. The graph paper has a Fahrenheit or Celsius scale on it, and the temperature is read where the ink line falls on the scale. The graph paper must be changed when it completes a full circle, usually weekly. Record the date on the graph paper when it is fitted and when you remove or change the graph paper. Keep old graphs as a permanent record of the performance of the vaccine storage unit. As with other thermometers, temperature readings should be checked and recorded at least twice daily.
Some chart recorders have temperature probes. (See “Temperature Probes” later in this section for more details.) Chart recorders are more difficult to read than digital thermometers because they require interpretation of the temperature graph.
4) Minimum and maximum thermometers
Min/max thermometers are available in fluid-filled and digital forms. They show the current temperature and the minimum and maximum temperatures that have been reached since the last time the thermometer was reset. Temperature fluctuations outside the recommended range can be detected by referring to the minimum and maximum temperature readings. It is important to manually reset the minimum and maximum temperatures to the current temperature each time the temperatures are recorded. The min/max thermometer must be reset regularly (after properly recording temperatures) for meaningful readings.
Figure 4: Min/Max Thermometers
5) Digital thermometers
Digital thermometers have a screen in which the temperature is displayed in Fahrenheit and/or Celsius. Choose a model that displays the minimum and maximum temperatures. Some models have a temperature probe and an alarm that can be set to ring at a specified temperature. An alarm that rings outside the storage unit is preferable to one that rings inside the unit. Some digital thermometers have two components: a display that mounts to the outside of the unit and a probe on a cord (usually 1 to 3 meters long) that is placed inside a vaccine or a diluent box inside the unit. This arrangement allows the temperature to be read without opening the door of the storage unit.
Digital thermometers with a min/max feature are easy to read because they display a number indicating the temperature and do not require interpretation. Temperature fluctuations outside the recommended range can be detected by referring to the minimum and maximum temperature readings. The digital thermometer must be reset regularly (after properly recording temperatures) for meaningful readings.
A limitation of min/max thermometers is that readings do not indicate when the exposure occurred and the exact length of time the vaccines were exposed to the out of range temperatures.
6) Thermometers that are not recommended for monitoring temperatures inside vaccine storage units: Fluid-filled biosafe liquid thermometers, bi-metal stem thermometers, and household mercury thermometers
Fluid-filled biosafe liquid (bottle) thermometers, bi-metal stem thermometers, and household thermometers are not recommended for temperature monitoring in vaccine storage units. They can be difficult to read and only indicate the temperature at the precise time they are read, therefore, temperature fluctuations outside the recommended range may not be detected.
Fluid-filled biosafe liquid thermometers, bi-metal stem thermometers, and household mercury thermometers are NOT recommended for monitoring temperatures.
Thermometer Placement
The thermometer should be placed in the center of the compartment away from the coils, walls, door, floor, and fan, and the temperature probe should be placed in the vaccine box. In the refrigerator compartment, the thermometer should be placed on the middle shelf adjacent to the vaccine. In the freezer, the thermometer should be placed on a box (or other item) adjacent to the vaccine so that it is in the middle of the compartment, not on the floor of the freezer. If the thermometer indicates a temperature outside the recommended range, remove the vaccine to an appropriate storage unit and check that the thermometer is appropriately situated.
Temperature Probes
Some chart recorders and digital thermometers have temperature probes. Probes are available in two forms: a standard probe and a biosafe liquid-encased probe. Probes should be placed in the center of the compartment. Fluid probes can give a more relevant reading because they do not react to short fluctuations in air temperature and mimic vaccine temperatures (1). To standardize procedures for domestic refrigerator temperature monitoring it is recommended that the temperature probe be placed in a diluent or vaccine box to reduce the risk of measuring short air fluctuations when opening the refrigerator door.
3.7 Thermometer Maintenance
Checking the Accuracy of the Thermometer
Thermometers should be checked annually to ensure:
- Temperature measurement is accurate.
- Batteries are functioning. Maintain and change batteries as recommended by the manufacturer, keeping in mind warranty requirements.
- Cables or probes are not damaged.
- An adequate supply of graph paper and ink pens for chart recorders.
Slush test
The accuracy of a thermometer can be checked using the following test. This test should be done at least once a year.
- Fill a polystyrene or plastic cup two-thirds with cold water. Place the cup in the freezer until a fine layer of ice forms on top and a small section of ice forms within the fluid (about 2 hours). If ice is present, this ensures the mixture is 0°C.
- Place the temperature probe in the middle of the cup (do not touch the sides).
- Observe the temperature after 2 minutes. The temperature should drop to 0°C within 2 minutes.
Most thermometers are calibrated to be accurate to ±1°C or better. If the temperature reading is more than 1°C above or below 0°C at 2 minutes, replace the battery and test again. If the thermometer is still not within range, contact your thermometer manufacturer for instructions regarding recalibration procedures or replace the thermometer.
Another method of testing thermometer accuracy is to test the accuracy of a thermometer against a reference thermometer but this is less reliable.
If the calibrated thermometer indicates an out-of-range temperature and if it is properly positioned assume it is accurate and take immediate steps to safeguard the vaccine. Once the vaccine is safely stored under proper conditions, the accuracy (and batteries) of the thermometer can be checked. However, always check other causes of inappropriate storage temperatures first.
Use the Monthly Vaccine Inventory and Refrigerator and Thermometer Maintenance in the Resources Section to summarize maintenance completed.
Thermometers should be checked annually to ensure:
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3.8 Cold Chain Monitors
General Principles
There are two basic types of cold chain monitors (CCMs): those that indicate whether packages have reached temperatures that are too warm and those that indicate whether packages have reached temperatures that are too cold. These types of monitors are designed to be irreversible indicators of inappropriate temperatures once a temperature excursion has occurred above or below the activation set points. In general, CCMs are for single use only and should not be re-used.
Cold chain monitors are not a substitute for twice-a-day temperature reading and recording. They should only be used to monitor the temperature of vaccine during transport.
Types of Cold Chain Monitors
Heat indicators
Heat indicators, also known as time and temperature indicators are made for single use only. Heat indicators that are appropriate for vaccine shipping have an activation temperature of +10°C and a run-out time of 48 hours to 7 days.
A heat indicator releases a coloured dye into the windows of the device when the temperature has exceeded the threshold or activation temperature (indicated on the device). The dye gradually moves through the windows over time. Once activated, the process is irreversible. If the temperature drops below the threshold again, the dye stops moving but does not disappear. Therefore these indicators also show the length of time in hours or days that the temperature has exceeded the desired range. Response cards are used to interpret the time and temperature relationship for each indicator.
The heat indicator must be preconditioned below its threshold response temperature before use; check manufacturer specifications for the length of conditioning time and the appropriate conditioning temperature.
In general, heat indicators are preconditioned in the refrigerator. This ensures that the dye inside the indicator is in a solid state when the activation tab is pulled. The activation strip needs to be removed to start the monitor—this allows for the coloured marker to melt and stain the porous wick as it undergoes temperature excursions above its threshold temperature. If the dye is not in a solid state, it will start moving down the track of the indicator and through the windows, producing an inaccurate reading.
Always attach the indicator to a vaccine vial or box; do not attach it to the transport box. If the surface to which the indicator is attached is at a temperature above the threshold of the indicator, the indicator will activate prematurely. Once the indicator is preconditioned, pull the activation tab, and place it and the vaccine into the environment to be monitored. This allows the indicator strip and reservoir pad to come in direct contact with each other and begins the temperature monitoring process. Like vaccines, heat indicators will have an expiration date and should be checked for these dates routinely.
Freeze indicators
Freeze indicators are made for single use only. Unlike warm indicators, freeze indicators do not indicate the length of time vaccine has been exposed to temperatures outside the recommended temperature range. Freeze indicators appropriate for vaccine shipping have an activation temperature of 0°C.
A freeze indicator uses coloured liquid to indicate exposure to freezing temperatures. In some models, the freeze indicator has a clear indicator bulb; when the temperature drops below the threshold freezing point, the indicator bulb irreversibly changes colour. The indicator does not require preconditioning and may be attached to any clean dry surface in the environment being monitored. There is no activation tab to pull; the indicator is working at all times.
Other freeze indicators use a specially designed ampoule filled with dye; when the temperature drops below the freezing threshold, the ampoule breaks and releases the dye that irreversibly stains the paper behind the ampoule. This type of freeze indicator requires preconditioning in a temperature above the freezing threshold; check the manufacturer's specifications for the duration of this preconditioning period. Leaving it out at room temperature will meet this requirement.
For freeze indicators that require preconditioning, attach the indicator to any clean dry surface in the environment being monitored, after the preconditioning. There is no activation tab to pull. To determine if the product has been exposed to freezing temperatures, observe the paper behind the ampoule. If it is stained with colour, the product being monitored was exposed. If there is no colour, remove the indicator from the surface to which it is attached and vigorously tap the bottom edge of the device three times on a hard surface. If the paper becomes stained, the product being monitored was exposed. Tapping will not cause colour staining in an unexposed indicator.
Like vaccines, freeze indicators have an expiration date that should be checked routinely.
Using cold chain monitors
Cold chain monitors are primarily used to monitor temperature thresholds when vaccine is shipped by manufacturers, commercial vaccine distributors, and government-managed vaccine depots. When the vaccine arrives at its destination, the CCMs should be checked immediately and the temperature inside the transport unit should be documented. If the CCM has been activated, the product should be quarantined in the fridge. Do not assume that the exposed vaccine CANNOT be salvaged. (See Section 6—Storage Troubleshooting for more details.)
Cold chain monitors should only be used during transport.
3.9 Vaccine Security
Protecting the Power Supply
To protect vaccine supply within the proper range, the unit must be in good working condition and have power at all times.
To prevent problems with the power supply
- Avoid using power outlets with built-in circuit switches and outlets that can be activated by a wall switch.
- Use a safety-lock plug or an outlet cover.
- Post a warning sign at the plug and on the storage unit alerting others not to unplug the unit.
- Label the fuses and circuit breakers to alert others not to turn off the power to the vaccine storage unit.
- Consider installing a temperature alarm with 24 hour and 7 days a week monitoring, especially for large vaccine inventories.
Temperature Alarms
A continuous-monitoring temperature alarm or notification system should be considered, especially for vaccine storage units with a large inventory, to help prevent substantial financial loss in the event of a cold chain break. These systems help alert staff to after hours emergencies. Simple systems sound audible alarms when the temperatures inside the storage units exceed the recommended ranges. A system that sounds an audible alarm and alerts one or more designated person(s) at a specified phone or pager number is preferable. For larger or centralized depots, alarms should be monitored 24 hours a day and 7 days a week by external sources that maintain a fan-out list of contacts. External monitoring services should be tested occasionally (like a fire drill) to ensure the service is able to function properly in the event of an actual cold chain break. This drill should be done outside of operational hours, for example, during a weekend when regular staff is unavailable.
Backup Generators
Facilities storing large vaccine inventories should install backup generators that automatically provide power to the storage units to maintain the recommended storage temperatures in the event of power outages.
Backup generators should be tested quarterly and should receive maintenance at least annually (check the manufacturer's specifications for test procedures and maintenance schedules). Backup generators should be of a sufficient capacity to run continuously for 72 hours if necessary. Plans should be made to ensure that an adequate supply of fuel is on hand. (See both Routine and Urgent Vaccine Storage and Handling Protocols in Section 2— Vaccine Storage and Handling Plans and Section 6—Storage Troubleshooting for more details.)
3.10 References
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Miller N, Watts M, Albances S et al. Technical issues with refrigerators. In: Langley A, Grant S, eds. Proceedings of the National Vaccine Storage Workshop. 1st ed. Brisbane: Queensland Health, 2004:15-42.
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Australian Government, Department of Health and Ageing. National vaccine storage guidelines: strive for 5. 3rd ed. Australia, 2005:7-23.
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Grassby PF. Safe storage of vaccines: problems and solutions. Pharm J. 1993; 251:323–327.
