Why temperature loggers, alarms, and VVM
labels are not enough
It is well known that
vaccines are temperature sensitive. They are easily inactivated by exposure to temperatures outside of the standard 2 oC
to 8 oC refrigerated storage range (1,
2). Both high and low
(freezing) temperatures cause inactivation, and recent reports show that for freeze-sensitive vaccines,
inadvertent freezing in the cold chain is a larger problem than heat
inactivation.
Temperature loggers, temperature alarms, and
VVM (vaccine vial monitors) have historically been used to monitor the
vaccine cold chain, and indeed this technology has greatly improved vaccine
safety and efficacy worldwide. Although highly useful, however, this
earlier technology has certain drawbacks. These drawbacks are:
Temperature
loggers must be downloaded and interpreted. This usually occurs
weeks or months after the cold chain break has occurred, and analysis
usually takes place far away from the problem area. Due to distance
and time, it is often difficult or impossible to locate the personnel
involved in the actual cold-chain break. As a result, corrective
action is slow and difficult, and much vaccine may be lost.
Temperature alarms that warn on preset values (e.g. freezing or high
temperature) are almost impossible to correctly set. They either warn
prematurely or too late, and give information of limited value. Thus
they tend to be disregarded.
VVM (vaccine vial monitors) were originally developed for heat-sensitive and freeze-tolerant vaccines such as OPV, and indeed were very useful for this purpose. However for many other vaccines, VVM may be a procrustean bed, because there can be significant differences between the stability properties of the VVM, and the stability properties of the vaccine. Thus in some cases, VVM may be too sensitive, and force users to throw out good vaccines too soon. In other cases, VVM are not sensitive enough. Many vaccines (such as diphtheria, haemophilis influenza, hepatitis B, inactivated polio virus, pertussis, and tetanus), are damaged by both freezing and heat, and VVM fail to warn about freeze damage. This is a widespread problem. Recent studies show that at present, freeze-sensitive vaccines run a high (75-100%) risk of being accidentally frozen at all stages of the cold chain, including early stages when the vaccines are still bulk packaged.
The ideal vaccine monitor?
The ideal vaccine monitor might have the
following characteristics:
Instantly warn when the cold chain breaks
(relative to a particular vaccine's stability)
Detect all cold chain problems, not just
elevated temperature
Accurately report vaccine stability -
report real problems, not just false alarms
Log (record) temperatures before and after
the cold chain break (for later analysis)
Be instantly customized to a particular
vaccine's time-temperature stability curve
Not require large amounts of
manufacturer's time and expense
Be capable of being implemented without
additional manufacturer effort
Not require large amounts of regulatory
review
Be easy to validate
Be simple, quick, and easy to implement
Consider the LifeTrack
The LifeTrack has all the features of the
"ideal" vaccine monitor listed above. Essentially the device combines
the best features of a temperature logger, temperature alarm, and VVM into a
new type of device that brings vaccine cold chain monitoring to a higher
level of flexibility, precision, and control. See our publication in
Vaccine.
Packaging the LifeTrack
Ideally one LifeTrack unit is packaged per
carton of vaccine vials. The unit should be attached to the carton by
a moderately strong adhesive, or as a subsection of the carton, so that the
linkage between the LifeTrack unit and the vaccine vials is maintained
throughout the cold chain. The LifeTrack unit should be added to the
vaccine carton as soon as possible after manufacturing, and should be left with the carton until
all the vaccine vials have been used.
Why carton-level monitoring is needed
The PATH studies of Matthias et. al. (Vaccine 25, p3980) show that "accidental freezing is pervasive and occurs across all segments of the cold chain. Between 14% and 35% of refrigerators or transport shipments were found to have exposed vaccine to freezing temperatures, while in studies that examined all segments of distribution, between 75% and 100% of the vaccine shipments were exposed." Thus most vaccine freeze-damage occurs while the vaccines are still in the carton! Carton-mounted LifeTrack units can detect this damage, while VVM can not.
To detect all damage, one possiblity would be a combined LifeTrack-VVM approach, combined with instructions that once the vaccines are removed from the LifeTrack-monitored carton, the vaccines should then be kept outside of the cold chain and monitored using the VVM.
Video discussion on YouTube
A copy of the talk: "Vaccine stability monitoring using the LifeTrack® electronic stability monitor", given at the 2nd Vaccine Congress in Boston on December, 2008, can be found on YouTube in three parts: Part 1, Part 2, and Part 3.
