Understanding the Fundamentals of Vaccine Vial Monitors

Published by Leo Almonte on

VVM Readings

Importance of Vaccine Vial Monitors

Vaccine Vial Monitors (VVM) are almost as important as the vaccine itself.  Understanding the fundamentals of vaccine vial monitors is essential. Vaccines are highly sensitive to heat. They lose potency once exposed to adverse temperatures during transport and storage. Too much heat or cold corrupts the composition of the life-saving vaccines and renders them useless.

Using impotent vaccines endangers lives since they may have ill health effects on their recipients. The World Health Organization has seriously addressed vaccine heat exposure, and cold chain personnel must not take the problem lightly.

Case Study of Exposed Vaccines: Cameroon

Researchers conducted a study in Cameroon to document the impact of vaccine exposure to adverse temperatures. As a tropical country with limited resources, the Cameroon pharma cold chain is exposed to fluctuating storage temperatures.A total of 65 vaccinating health facilities were visited for the study from eight health districts. Of the health facilities, 48 (73.8%) were governmental facilities. About 50 (76.0%) of the facilities had a functional thermometer. Among the 50 health facilities with a functional thermometer, abnormal temperatures were registered in 10 (20%) health facilities during data collection and 12 (24%) in the 2 months preceding collection. Another factor significantly associated with abnormal temperature recording was the absence of an alternative power source.

potential factors for vaccine exposure to temperature excursions
Table 1 Potential factor associated with the exposure of vaccine to abnormal temperature. (Source: Yakum, M., Ateudjieu,J.,Pélagie, F.R., Walter, E.B., and  Watcho)

The study showed that vaccine exposure to abnormal temperatures was associated with the absence of an alternative power supply. To address this problem, each vaccinating facility in the North West region must have at least two power supply sources. 

Researchers conducted the study in eight health districts in Bamenda, Benakuma, Kumbo West, Ndop, Ndu, Nkambe, Tubah, and Wum Health Districts.  

The study showed that 24% of the vaccine refrigerators exposed vaccines to sub-optimal temperatures within a two month period. The problem of overheating was documented in all refrigerators that were exposed to sub-optimal temperatures, whereas only 67% of them were exposed to freezing temperatures. The absence of an alternative source of power supply was associated with vaccine exposure to sub-optimal temperatures.

The study concluded that vaccine exposure to sub-optimal temperatures is a global problem and has been well-documented in many parts of the world. 

Vaccine Vial Monitors: How They Work

At the very least, VVMs can prevent exposed vaccines from being used, thereby, protecting recipients from health hazards. The simple technology applied to VVM fills in a huge gap in the pharma cold chain issues, especially in countries where refrigeration and power supply are problems. 

A vaccine vial monitor (VVM) is defined as “a label containing a heat-sensitive material which is placed on a vaccine vial to register cumulative heat exposure over time.”


The VVM is represented by a circle with a small square inside,  printed on a product label attached to the cap of the vaccine tube or around an ampoule’s neck. It contains a light heat-sensitive material, in the shape of an inner square that becomes darker when exposed to heat. 

The dual effects of time and temperature cause the VVM’s inner square to darken, irreversibly, in a gradual manner. The degree of color change indicates how much exposure to improper temperatures has occurred. 

The vaccine should be discarded when the inner square becomes as dark as the outer circle. This means that the vial has been exposed to an unacceptable degree of heat. Once the inner square’s darkness is the same as, or darker than the outer circle, the health worker must discard the vaccine. 

Different Types of  Vaccine Vial Monitors 

There are four different types of VVMs for specific vaccines, which are as follows:

VVM classification types
Table 2: VVM reaction rates by category of heat stability ( Source: WHO, 2002)

 General Information on Vaccine Vial Monitor

Physical Appearance of the VVMs

Rule 1: If the inner circle has a lighter shade than the outer circle, the vaccine may be used

Rule 2: If the inner circle is the same shade or darker than the outer circle, the vaccine must be discarded

Color Change and Exposure

Vaccine Vial Monitors will not darken immediately when exposed to a temperature above  8°C, outside the cold chain, for a limited amount of time. Vaccines can withstand such temperatures due to their ability to remain stable during brief exposure to moderate heat. The inner square changes density during prolonged exposure to heat.

Instructional for Vaccine Vial Monitor  (Source: WHO, 2002)

Vaccine Refrigeration

The VVM will not reverse its darkening if it is returned to the refrigerator since the darkening is irreversible. VVMs show the accumulated heat exposure that the vaccine has undergone.

The Vaccine Vial Monitor is not affected by freezing temperatures, since it only reacts to increases in heat.

Quality Control and Testing

Health care workers test each batch of Vaccine Vial Monitors two times to ensure they correctly respond to heat exposure. They do the first test before shipment from the factory. Manufacturers conduct the second before dispatch. Medical technologists use color reflectance densitometers to test the Vaccine Vial Monitors.

Vaccine Vial Monitor and Expiry

Vaccine Vial Monitors indicate if vaccines are compromised due to prolonged exposure to sub-optimal temperatures. However, vaccines that pass their expiry dates cannot be used for immunization even if the VMMs show that they are not exposed to adverse heat. 

It is important to note that Vaccine Vial Monitors do not change the vaccine’s tolerance to heat, they only indicate exposure to heat.

Vaccine Vial Monitor and Cold Chain Management

Vaccine Vial Monitors contribute to the pharma cold chain’s efficient management, especially at the ground level. Medical health workers can select vials with minimal exposure, for use. 

VMMs also enable handlers to track which storage places have unstable cooling systems, based on the indicators’ density. They can check the thermal systems effectiveness if they see the change of density during transport or storage. 

Medical health technicians can also prioritize using vaccines with the darker squares, and use the ones with lighter shades after, as long as the squares do not display densities darker than the surrounding circle. 

Protocols and Evaluation on Proper Use of Vaccine Vial Monitors

The World Health Organization encourages the facilitation of Knowledge, Attitudes and Practices (KAP) based on standard protocols. WHO participates in this evaluation to:

•       Know if health workers are interpreting VVMs readings correctly

•       Verify if VVMs are handled correctly

•       Record vaccine wastage due to hear exposure

•       Give awareness to any negativity surrounding VVM use  

The WHO, local government, and health agencies require proper training for key personnel involved in handling vials such as stock managers, workers who transport vaccines, health workers, and National Immunization Day volunteers.


Vaccine Vial Monitors are an added cost that affects the price of vaccines. The increased cost, however, is compensated for by reductions in wastage, health risks, and inefficiencies of cold chain management.  

Before the invention of Vaccine Vial Monitors, health workers had no way to accurately assess whether vaccines had been compromised by exposure to heat. Vaccines have no visible change in appearance when they are overexposed to heat.

After a systems breakdown when cold storage is interrupted by a lack of power supply or malfunctioning refrigerators, health workers are trained to discard all the vaccines in storage. Such wastage can be avoided with the use of  Vaccine Vial Monitors to determine if vaccines have been compromised. Reducing guesswork can reduce wastage and financial loss, while maintaining vaccine safety.

It is truly amazing how a small label, with a small circle, with a square in the middle, saves lives and wastage in the cold chain. 


World Health Organization, (2002) ,accessed from from http://www.vaccineresources.org/files/Getting_started_with_VVMs.pdf

Yakum, M., Ateudjieu,J.,  Pélagie, F.R., Walter, E.B., and  Watcho, P. (2015) Factors associated with the exposure of vaccines to adverse temperature conditions: the case of North West region, Cameroon, accessed  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4485865/


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