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  1. Larry Schlussler
  2. Cold chain equipment
  3. Tuesday, 26 May 2015
How about a Buffered Temperature Chain (BTC)?
Vaccines which are highly thermally stable can be distributed in the Controlled Temperature Chain (CTC). To be incorporated into the CTC the vaccines must be stable enough to be stored for 3 days at 40 deg C. There are very few vaccines which are this stable. If vaccines can be incorporated into the CTC there are numerous logistical and financial advantages. Since the infrastructure is much simpler and less expensive. Establishing a “Buffered Temperature Chain”, BTC could have many of the advantages of a CTC. The BTC would keep temperatures below 28 deg C.
Simple low cost methods could be incorporated to keep vaccines below 28 deg C. The expected life of vaccines of varied temperature sensitivity is given in the table below.
Category No. days to end point at 28 deg C
VVM 30 (High stability) 100 days
VVM 14 (Medium stability) 50 days
VVM 7 (Moderate stability) 25 days
VVM 2 (Least stable) 7 days
This data was derived from the Arrhenius graph showing Temperature Dependence. The graphs were obtained from “Temp Time” a VVM manufacture.
An Mean Kinetic Temperature (MKT) temperature of 28 deg C was choosen because it could be obtained passively by combining evaporative cooling, insulation and thermal mass in simple low cost coolers.
The VVM graphs are based on MKT temperature. The effect of temperature excursions could easily be monitored by a resettable direct reading MKT thermometer. Using a direct reading MKT thermometer simplifies data analysis. See Tech Net Post (http://technet-21.org/en/forums/vvm-mkt-equivalent-and-complementary-concepts/likes). Data is much easier to analyze when using a MKT thermometer rather than a data logger; the effect of temperature excursions can be seen from a single number.
The color change on a VVM is based on MKT temperature. The MKT thermometer could also indicate if temperatures strayed over 40 deg C which may be harmful to the vaccines even if the MKT temperature remains below 28 deg C.
If there is interest in the Buffered Temperature Chain, Sun Frost could provide direct reading MKT thermometers and temperature buffered storage containers. The containers could be built for portability or for use in a clinic.
Larry Schlussler, Ph.D.
Sun Frost
Larry Schlussler Accepted Answer
Dear John,
Thanks for your thoughts on the “Buffered Temperature Chain” (BTC).
What we were presenting is two separate concepts, perhaps that was not clear. The first was the implementation of some simple cooling techniques to extend the life of a vaccine. These techniques could keep the vaccines below 27 deg C. I’m not trying to suggest that the BTC would replace the Controlled Temperature Chain. The CTC is valuable for more temperature stable vaccines.
The Arrhenius graphs show how the life of a vaccine changes with temperature, a graph for a moderately stable vaccine, VVM 7 is attached. If VVM 7 vaccine is kept at 27 deg C its life will be 30 days. Since this data is available the use of the BTC would not require recertification.
The second concept we presented was a monitoring technique using MKT temperature. A direct reading of MKT thermometers can simplify data analysis. Currently the performance of a cold chain vaccine storage refrigerator in a clinic is often monitored by a data logger. Even though the vaccines in the refrigerator contain VVM indicators it is useful to look at the variations in storage temperatures to evaluate the performance of the refrigerator. If a manager receives a graph showing the temporal temperature variation in the refrigerator for the past month there is no simple way to say how the temperatures variation effected the life of the stored vaccines. Perhaps the door of the refrigerator was left open 4 days that month and the temperature increased from 5 deg C to 20 deg C. Would that scenario be problematic? If the manager had a direct reading MKT thermometer it could readily be seen that the MKT temperature for the month remained below 8 deg C and that these temperature excursions did not significantly effect the life of the vaccine. A second continuously updated 24 hour rolling average direct reading MKT thermometer could alert a manager of a significant short term excursion. The thermometer would look at a window of the past 24 hours and the data would be updated every 15 minuets. An MKT thermometer would buffer out short term temperature changes which would not effect the stored vaccines.
For a vaccine carrier a direct reading MKT thermometer would be valuable in evaluating the performance of the carrier itself. For example, say on a 4 day trip the temperature in the carrier started in the cold chain at 5 deg C and its temperature increased linearly to 27 deg C. The average temperature would be 16 deg C and the MKT temperature for the trip would be 18 deg C. From the attached Arrhenius graph the life of the VVM 7 vaccine at an MKT temperature of 18 deg C would be about 105 days. On this excursion the vaccine lost only 4% of its life. It could be concluded that under these conditions the performance of the carrier was quite adequate, and the vaccine is still safe to use.
Again the basic idea of the BTC is to keep the vaccines cooler by simple low cost means so that their life is extended. If vaccines become less heat sensitive the BTC will become more useful for long term storage.
Sincerely,
Larry Schlussler, Ph.D.
Sun Frost
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  1. more than a month ago
  2. Cold chain equipment
  3. # 1
John Lloyd Accepted Answer

This Posting proposes the concept of a ‘Buffered Temperature Chain’ (BTC) instead of a ‘Controlled Temperature Chain’ (CTC). The BTC concept uses the Mean Kinetic Temperature (MKT) reading set to +27C to predict the effect of excursions of temperature on vaccine. The concept of MKT, though used by equipment test laboratories, remains complex to grasp by managers.

But my main issue with this proposal is that if we adjust our expectations a little, we may not need either CTC nor BTC in our armoury of tactics to take vaccine to the last 20% of children, most of whom live in areas of difficult access and other extreme conditions.

First, we can adjust the inference in the posting that CTC vaccines may be distributed out of the cold chain at any or all stages of distribution. We could be content with taking vaccines ‘beyond the reach of the cold chain’, assuming this practice is limited to the most remote and difficult destinations where the cold chain cannot reliably maintain recommended storage temperatures.

Second in our drive for equity, we can remind ourselves that our rationale does not only apply to individual vaccines used in Supplementary Immunization Activities (SIAs), but also to routine outreach services offering a range of vaccines. We would prefer to avoid the certification of specific, new vaccine products as CTC-qualified because distributing several versions of the same vaccines adds to complexity of distribution.

Finally, the accuracy of each VVM type (recently enhanced by a high temperature threshold indicator), that are matched to vaccine products has been extensively verified and an agreement to start using them was reached between WHO, UNICEF, manufacturers and regulators many years ago. On the understanding that vaccines are kept in the cold chain until used, in the event of a failure of cooling, they may be administered without a critical loss of potency if the VVM has not triggered. In other words, if a health worker walks to a remote outreach site with a vial of Tetanus vaccine – for example – he/she may administer the vaccine if the VVM has not triggered. The vaccine may be administered even if the icepacks melted some time ago and when the vaccine is at an ambient less than the threshold indicator.

Free of either the restrictions of pre-qualification required for CTC or the interpretation of MKT, we can already use vaccines ‘beyond the cold-chain’ . The immunisation manager has provided the maximum cold chain protection that is feasible in the circumstances, but will not be prevented from using the vaccine beyond the cold chain to the limits of the stability of the vaccine. This works for most vaccines except for lyophilized vaccines including measles that, once reconstituted must be kept cold.

John Lloyd,

Supply Chain Consultant, France

  1. more than a month ago
  2. Cold chain equipment
  3. # 2


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