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: