Imagine that VVM’s do not exist. As an alternative a tiny electronic device could be developed which would record the temperature history of the vaccine vial. The device would be attached to the vial and graphically display the temperature history of the vaccine. If a health worker wanted to know how the temperature history of the vaccine would affect its life, how would they do it? This is essentially the same problem faced when trying to interpret the data obtained from a refrigerator or vaccine carrier data logger. Currently there is no analytic method to determine how temperature excursions affect the life of a vaccine.
A VVM may be thought of as an analogue device whose function is governed by the Arrhenius rate equation. The output of this elegantly simple device is a displayed dot of varying density. The density of the dot indicates the percent of life left in the vaccine. If VVM’s were not available the electronic device attached to the vaccine vial could use the collected data to calculate how temperature variations affected the life of a vaccine. This calculation could be done with the aid of the Arrhenius rate equation. The display of this device could mimic a VVM by displaying a dot of varying density to indicate how much vaccine life is left. However with digital electronics it may be more informative to display the number of days of life left. This same analytic tool could be used to interpret the data recorded on a refrigerator or vaccine carrier data logger. This would be a major step forward since there is no analytic method currently in use to determine how temperature excursions effect the life of a vaccine.
Knowing how temperature excursions affect the life of a vaccine can lead to more intelligent and responsive alarm systems. WHO recommends that an alarm is turned on when temperatures rise above 8C for 10 hrs. This recommendation could be misleading an alarm could be turned on when there are no problems and not turned on when there are serious problems. For example, for a 24 hours day an excursion to 9C for 11 hrs., then a return to 5C for 13 hrs. would turn an alarm on however this excursion would not lower the expected life of a vaccine. On the other hand if each day the temperature climbs to 20C for 9 hrs. in the afternoon, and than returns to 5C for the remainder of the day the alarm would not be activated, however the life of the vaccine would be cut in half.
A DIGITAL ANALYSIS OF TEMPERATURE DATA BASED ON THE ARRHENIUS RATE EQUATION WOULD HAVE THE FOLLOWING ADVANTAGES:
- Simplified data interpretation: The analysis would show the effect of a temperature excursion in a simple to interpret form.
- The severity of a refrigerator problem would be indicated which is a valuable piece of information for management.
- Elimination of false alarms: Alarms would coincide with indication from a VVM.
- More responsive alarm systems.
- Reduced vaccine waste.
- Data to show that outreach programs can be safely extended.
- Simpler and less expensive designs for refrigerators without sacrificing vaccine life
These advantages could come to fruition if we simulated digitally what a VVM does in an analogue fashion.