What is a Vaccine Vial Monitor and How Does it Work?

Health Worker using a VVM In practice

A Vaccine Vial Monitor (VVM) is a label containing a heat-sensitive material that is placed on a vaccine vial to register cumulative heat exposure over time. The combined effects of time and temperature cause the inner square of the VVM to darken gradually and irreversibly. The rate of color change increases with temperature.

The VVM is affixed to a vaccine vial by the vaccine manufacturer to allow for full-life heat monitoring. It allows health care professionals to administer vaccines, confident that the vaccine has not been exposed to potentially damaging heat. Even if a vaccine was exposed to an inadvertent heat excursion, the VVM provides a visual cue if the vaccine could still be used and it’s use can help reduce wastage and increase coverage.

Since a VVM and the vaccine move through the supply chain together, they are exposed to the same conditions as measured by Mean Kinetic Temperature (MKT). This allows the VVM to give healthcare workers an overview of the cumulative heat exposure of the vaccine and a clear indication when it has reached its time-temperature end point. 

VVMs are time-temperature indicators that give visual warning of potentially damaging cumulative heat exposures and indicate to healthcare workers whether a vaccine can or cannot be used.

How does a VVM work?

The inner square of the VVM is made of heat-sensitive material that is initially light in color and becomes darker when exposed to heat. The inner square is lighter in color than the outer circle prior to heat exposure and remains so until the heat exposure reaches a level that surpasses the approved stability limits of the vaccine.. At the discard point or endpoint, the inner square is the same color as the outer circle. This indicates that the vial has been exposed to an unacceptable level of heat. The inner square continues to darken as heat exposure continues until it is much darker than the outer circle. If the inner square becomes as dark as or darker than the outer circle the vial must be discarded.

What does a VVM look like?

The VVM is a circle composed of both a reference ring and a small inner square, called the active square or active surface. The VVM may be printed onto a product label, or it may be attached as an independent device onto the cap of a vaccine vial or tube, or to the neck of an ampoule. See image below:

Visual Image of the heatmarker VVM30 poster

How to read the VVM

VVM’s gradual and permanent color change from light to dark shows the temperature history of the vaccine from the time the VVM is affixed to the vaccine vial by the manufacturer – until the product is used. The inner square of the VVM is made of heat-sensitive material that is initially light in color and becomes darker when exposed to heat. The color change is faster at higher temperatures and slower at lower temperatures. At the endpoint, the inner square is the same color as or darker than the outer circle.

To read a VVM, compare the color of the inner square to the color of the outer circle:

Rule 1: If the inner square is lighter than the outer circle, the vaccine can be used provided that the expiry date has not passed.

Rule 2: If the inner square is the same color or darker than the outer circle, the vaccine must not be used.

Visual Image explaining to users how they should read a VVM

What does a VVM look like as it changes color?

The graphic below shows the changing appearance of the VVM as it is exposed to heat over time:

Visual Image showing what a VVM looks like when it changes color

How are VVMs measured?

To measure VVMs, place the VVMs with the release liner still attached onto white card stock, then measure the Optical Density (OD) of the active indicator (I) and reference ring (R) using an X-Rite 500 series spectrodensitometer or equivalent. Measure the reference ring by taking one measurement from the bottom of the ring and a second measurement from another point 90° away. Measure the active indicator by taking two measurements from different points within the active square. To determine optical density difference, also called R-I, subtract the average I value from the average R-value.

How should VVMs be stored?

Prior to being applied to vaccines, VVMs must be stored at temperatures < -24°C and kept away from light and other sources of radiation. Once applied to vaccines, storage conditions are based on the vaccine’s storage requirements.

What are the benefits of Vaccine Vial Monitors?

VVMs help to expand the reach of immunization programs to remote populations and to minimize the risk of people receiving potentially ineffective, heat-damaged vaccines along with increasing the efficiency of immunization programs worldwide.

The VVM is a critical component of vaccine manufacturers' ability to supply life-saving vaccines in support of global vaccination programs. Through a simple, predictable, reliable, and visual color change, healthcare professionals know at a glance whether a vaccine has been exposed to potentially damaging heat. Irreversible time-temperature indicators can play a vital role in the success of vaccination programs worldwide.

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