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
Sun Frost
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