Thermal analysis of refrigeration systems used for vaccine storage

Abstract

Each year, billions of dollars of vaccines are stored in refrigerators at the facilities of a variety of medical providers. Many vaccines must be maintained in the range 2 °C to 8 °C to retain product potency. We have tested the performance of two types of refrigerators to determine if these refrigerators are suitable to this task, and to identify proper storage and temperature monitoring methods. Nineteen calibrated Type T thermocouples, distributed through the refrigerator interior, served as reference thermometers. Attachment of thermocouples directly to vaccine vials gave accurate measurements of the vaccine temperature, which often differed from the air or interior wall temperatures during door openings or defrost cycles. A household type dual-zone refrigerator/freezer [refrigerator compartment capacity = 0.400 m 3 (14.13 cu. ft.)] and a pharmaceutical grade refrigerator [capacity = 0.489 m 3 ] proved fully adequate at maintaining vial temperatures within the desired 2 °C to 8 °C range, independent of how the refrigerator was loaded. Tests of intermittent and continuous door opening and of simulated power outages demonstrated the value of adding water bottles to the door as a thermal ballast in the dual-zone refrigerator model. We tested five electronic data loggers as a means of continuously logging refrigerator temperatures. Properly located, data loggers and temperature monitors accurately monitored vial temperatures for extended periods.

Thermal Analysis of a Small Pharmaceutical Refrigerator for Vaccine Storage

“…This information is reported in table 4 below. These results are similar to those obtained in power outage trials of the large pharmaceutical refrigerator unit [2]. During a power outage event, both the small and large pharmaceutical grade refrigerators warmed up to temperatures above 8 °C much more quickly than the household grade units that were tested.…”

“…This study supplements our previous refrigerator studies of dormitory-style, freezer-less, dual-zone and large pharmaceutical grade refrigerator units [1,2]. We have followed the same approach as in our preceding studies, installing 19 NIST-calibrated, Teflon-insulated, Type T thermocouples in various locations inside the refrigerator to determine the spatial temperature distribution throughout the unit's interior.…”

Effectiveness of a web-based education program to improve vaccine storage conditions in primary care (Keep Cool): study protocol for a randomized controlled trial

“…The most sensitive vaccines are hepatitis B vaccines with a freezing threshold of -0.5 °C [ 2 ]. A thermal analysis of frequently used types of refrigerators by the US Department of Commerce [ 22 , 23 ] showed that vaccine vial temperatures vary depending on the refrigerator type, loading density and location of vaccines inside the refrigerator. Typical refrigerators used in German primary care are the types “freezerless” (single refrigerator compartment without a freezer) and “dual zone” (separate compartments for refrigerator and freezer, both with individual doors), both so-called domestic refrigerators.…”

“…Typical refrigerators used in German primary care are the types “freezerless” (single refrigerator compartment without a freezer) and “dual zone” (separate compartments for refrigerator and freezer, both with individual doors), both so-called domestic refrigerators. Based on different scenarios, that is, door openings and loading density, temperatures can vary by +/-2.3 °C in the type “freezerless” and by +/-4.5 °C in the type “dual zone” [ 22 , 23 ]. The maintenance of the temperature range of +2 to +8 °C, as recommended by vaccine manufacturers and public health authorities worldwide, is hence justified and therefore serves as a primary outcome measure.…”

Improving Vaccine Safety by Using an Algorithmic Model as a Replacement for a Physical Thermal Buffer

“…1 To ensure that vaccines are not damaged or compromised the Centers for Disease Control and Prevention (CDC) have issued protocols to ensure proper handling, which specifies that the temperature of stored inventories must be regularly and accurately monitored to ensure that the vaccine temperature remains within specified limits. 2,3 Temperature monitoring is complicated by the fact that the raw data received by the thermistor in the refrigerator can be misleading. An unweighted temperature probe e.g.…”