Vaccine stability monitoring

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.

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