Vaccine Temperature Monitoring Devices in the Supply Chain

For vaccines to be effective and of good quality, vaccine temperature monitoring should be a top priority. Temperature plays a vital role in the vaccine’s effectiveness. Temperature-monitoring devices in the vaccine supply chain are essential to minimize temperature excursions and check the viability of vaccines. A hot environment accelerates potency loss while freezing clumps chemicals making the vaccine less effective. Just the right temperature for the right kind of vaccine is the best practice. Typically this would be between 2°C to 8°C (35°F to 46°F).

The sensitivities of each vaccine will indicate how they should be handled. Some vaccines are freeze-sensitive, others are not. Some vaccines are heat-stable, but others react more quickly when exposed to elevated temperatures.

Being knowledgeable about the vaccine in transport is the first step. The second is getting the vaccine containers and locations equipped with temperature sensors. To gauge the temperature, several devices are available in the market, each performs unique tasks required for specific vaccines. The devices can be used to monitor fixed storage locations, during transport, or both.

Monitoring heat exposure

Vaccine vial monitors (VVMs)

VVMs are the only temperature-monitoring devices that accompany the vaccines throughout the supply chain. A VVM is a label containing a heat-sensitive material. Placed on vaccine vials, it records cumulative heat exposure over time through a gradual change in color. The change in color of the box inside the circle indicates the effectivity of the vaccines. If the color of the box is the same as the outside color or darker then the vaccine should not be used. VVMs only measure heat exposure, thus not applicable to cold temperature.

VVM Types and Reaction Time

There are four types of VVM. The table below shows the reaction rates of different types of VVM at three different temperatures. Manufacturers use a different VVM depending on the stability of the produced vaccines.

The main purpose of VVMs is to ensure all administered vaccines are potent and not heat-damaged. It also proves helpful when cold-chain breaks happen, to show which vaccine can be used and which should be discarded.

Monitoring International Vaccine Shipments

Cold Chain Monitor (CCM)

CCM cards are used for oral poliovirus vaccines (OPV) packed in dry ice and shipped internationally. Like VVM, this device records cumulative exposure to heat. Positions marked A, B, C signify the length at which the vaccine has been exposed to specific temperatures. A spot of blue ink will stain these marks, and once it reaches D, then the temperature has reached above 34°C (93°F). Cards are provided and temperatures are recorded from the manufacturers to the supply stores.

Electronic Shipping Indicators

This device records temperature every 10 minutes for 20 days. They provide digital displays and alarm set-up for temperature range. The range demonstrates the heat and freeze – sensitivity of the vaccines. Once an excursion occurs, the alarm goes off. Some brands can download temperature data to a computer for record monitoring.

Vaccine Temperature Monitoring in Primary and Subnational Stores

Primary and subnational stores contain lots of stocks that amount to millions of dollars. The use of continuous vaccine temperature monitoring devices might be expensive, but it will offset a possible future loss in case of temperature excursions damaging the products.

Chart Recorders

Chart recorders are electromagnetic devices that measure temperature. However, WHO no longer advises the use of this device as they are prone to mechanical failure; and data cannot be stored and analyzed on the computer. 

Programmable electronic temperature and event logger systems

This is a sophisticated system used in most primary and subnational stores. Temperature sensors are placed in every cold room and freezer room, vaccine refrigerator, or vaccine freezer where they are directly linked to a central computer-based monitoring point via wired or wireless connections. Central data storage allows temperature records to be analyzed electronically. The system can also be manipulated to produce periodic reports.

Some of the systems are equipped with sensors that monitor frequent door opening, humidity, voltage fluctuations, and alarms that send alerts to responsible staff via auto-dialer, email, and SMS-enabled devices. Intranet and Internet connectivity also provides remote monitoring.

The figure below illustrates the typical setup for some of the options above.

Fixed Gas or Vapor Pressure-Dial Thermometer

When the power supply breaks, most sensors connected to it will not function and not gather data. That’s why having this particular device as a backup is a must. Because it does not require a power supply, using it is a fail-safe option. However, this should not be used as a substitute for a programmable set of sensors, as these are not accurate and cannot be analyzed electronically.

D. Monitoring in Small Subnational and District Stores and Health Facilities

Small subnational and district stores have one or more vaccine refrigerators or vaccine freezers. The table below shows what’s the appropriate devices to be used for either vaccine refrigerators or freezers.

30-day Electronic Temperatures Recorder

This device is placed inside the refrigerators where they log temperature at 10- minute intervals or less for 30 consecutive days. It also displays a 30-day history of heat and freeze-alarm violations. Alarms get triggered when the temperature drops -0.5°C (31°F) or below for 60 minutes or if it exceeds +8°C (46°F) for a continuous period of 10 hours.  The device displays OK or a tick symbol if the temperature stays within the recommended range. Most newer models allow for downloading of data and can be uploaded to a computer where the data can be analyzed. This device is not suitable for freezer rooms or freeze boxes.

Electronic Freeze Indicators

These are small digital devices that are placed with freeze-sensitive vaccines during transport or storage. Same with an electronic temperatures recorder, this device displays whether or not the vaccines have been exposed to freezing temperatures using an alarm set-up. Once the alarm goes off, the device is no longer usable.  Otherwise, the device can still be used until the battery runs out.

Integrated digital thermometer

Typical vaccine refrigerators and freezers are equipped with this device. Using the internal temperature sensor, it can monitor the coldest point in the vaccine storage. Instant reading and displaying of temperature are this device’s biggest advantages.

Stem Thermometers

Even though they provide instantaneous reading like the device above, WHO no longer recommends the use of stem thermometers as a primary device, rather a backup as they don’t rely on a power source to run. However, they remain the primary device of vaccine freezers not connected to a programmable electronic temperature and event logger system.

Aside from the devices listed above, WHO no longer recommends bimetallic dial thermometers because of its unreliability. It loses calibration over time especially when dropped.

Monitoring Transport Temperatures

Apart from stores and manufacturing, the transport process can also be problematic without the right sensors. Most of the devices used in transport are the same devices used during storage, like the devices mentioned. Plus, pharma logistics need to have a cab-mounted display and printer unit with a thermal printer option. The printout provides a hard-copy arrival record for the receiving store and shows the vaccine’s transport temperature history.

Below is a table that lists devices in order of preference, separated with and without freeze-sensitive vaccines. The upper table shows monitoring devices’ inboxes and carriers. The bottom table shows the monitoring devices used in refrigerated vehicles.

The possibility of vaccines being ineffective is serious. After all, it takes time, effort, and money to administer one. We don’t want to waste all the effort by injecting a vaccine that is ineffective. Following the guidelines written above will reduce the risk. Using the right device, of the highest quality, and from a trusted manufacturer will set out a smooth process for those involved in the vaccine supply chain.