Thermal Analysis of Refrigeration Systems Used for Vaccine Storage Michal Chojnacky National Institute of Standards and Technology Process Measurements Division Gaithersburg, MD michalc@nist.gov Project funded by the Centers for Disease Control and Prevention CDC Contact: Tony Richardson, Public Health Advisor
Current Problem CDC administers ~ $3 billion of vaccine through Vaccines for Children (VFC) program each year Storage temperature control is vital to maintaining vaccine potency – Storage outside 2 °C to 8 °C range can render vaccines ineffective – A meta-analysis estimates 14 to 35% of delivered vaccines are subjected to inappropriate storage temperatures Social and economic costs of improperly stored vaccines – Cost of manufacturing and delivering vaccine wasted – Vaccine delivery delayed – Reported vaccination rates are erroneously high – Recipients are not protected $3 B/yr program X 30% loss due to known thermal excursions = $900 M/yr loss
Background and Purpose Challenges in ensuring VFC providers follow good vaccine storage and temperature maintenance practices – 45,000+ providers, many different storage and temperature monitoring methods – Suitability of commercial refrigerators for vaccine storage not well documented – Impact of refrigerator loading pattern, normal refrigerator use, environmental temperature fluctuations, …unknown! – Inadequate temperature monitoring: improper thermometer placement, possible device inaccuracies, and absence of continuous temperature data collection Need for research that matches everyday conditions experienced by vaccine providers – Improve storage and handling guidelines and practice
Experimental Method: Measurement System 19 thermocouples and 3 to 6 electronic data Device name: U(k=2), C loggers arranged throughout refrigerators Thermocouple measurement system 0.12 – Calibrated at ice point (0 °C) Data logger A 0.58 – Sensors attached to vaccine vials , walls, Data logger B 1.41 inside glycol-filled bottles, and hanging in Data logger C 0.67 air Data logger D 0.59 – Recorded data continuously during trials lasting 15 hours to several days Data logger E 0.59 Rate of data collection – Thermocouples = 10 s – Data loggers = 30 s to 1 min 100,000 – 500,000 data points collected during each trial – Complete picture of temperature behavior over time – Condense into representative samples and averages to find correlations between tested criteria and temperature trends
Experimental Method: Tested Criteria 4 refrigerator styles – Freezerless, Dormitory-style, Dual Zone Fridge/Freezer, Pharmaceutical grade Varied refrigerator loading patterns – Low, medium, and high density loads – Plastic trays, cardboard boxes, and combined trays/boxes storage configurations – With and without water bottles (3 - 5% total capacity) in refrigerator door Normal use simulation - open / close refrigerator door Increased room temperature Power outage and recovery
Results: temperature stability of refrigerators Freezerless Refrigerator Dual Zone Refrigerator 9 9 8 top wall 8 Average temperature, °C 7 7 Average temperature, °C 6 6 5 5 4 4 3 3 2 2 1 back of tray, near wall near cooling unit 1 0 0 empty lowtrays medtrays I medtrays II medtrays bottles medboxes bottles highboxes bottles lowmixed bottles medmixed bottles highmixed bottles highmixed bottles opendoor medmixed medmixed opendoor lowtrays empty medtrays medtrays bottles medboxes bottles highboxes bottles lowmixed bottles medmixed bottles highmixed bottles highmixed bottles opendoor medmixed medmixed opendoor data collected over 26 day period 51 days Dorm-style Refrigerator Pharmaceutical Refrigerator 12 9 10 8 8 7 Average temperature, °C Average temperature, °C 6 top wall 6 4 2 5 0 4 severe set point -2 3 drift after 2 weeks -4 2 -6 1 -8 -10 0 lowtrays medtrays medtrays bottles medboxes bottles medtrays bottles highboxes bottles lowmixed bottles medmixed bottles highmixed bottles highmixed bottles lights out highmixed bottles opendoor medmixed medmixed opendoor lowtrays lowtrays opendoor empty empty II lowtrays medtrays medboxes highboxes highboxes II lowmixed medmixed highmixed highmixed opendoor medmixed medmixed opendoor 45 days 31 days
Comparison of Refrigerator Performance in Response to Tested Criteria I. Loading density Little or No Impact Negative Impact on Performance FREEZERLESS DUAL ZONE • Possible minor increase in location-specific temperature variation for high density loads DORM-STYLE PHARMACEUTICAL • Noticeable impact on performance due to lack of air circulation • High-density loading patterns increased location-specific temperature variation Density variation pattern in dorm-style fridge
II. Opening/ closing refrigerator door Little or No Impact Negative Impact on Performance DORM-STYLE PHARMACEUTICAL • Vial temperatures not significantly affected • Most sensors record brief temp increases, overall decrease • Exacerbates already poor temperature control DUAL ZONE High Density Mixed Load With Bottles 9 • Small increases in vial temps, but 8 remained within 2 °C to 8 °C 7 Temperature, °C 6 (vial - floor) 6 10 (in box) 11 (in box) 12 (vial - mid) FREEZERLESS 5 13 (vial - mid) 17 (glycol - floor) 4 18 (glycol - mid) • Small increases in vial temps, but 19 (glycol - top) 3 20 (vial - low) remained within 2 °C to 8 °C 2 1 • Water bottles in door reduced temperature 0:00 0:15 0:30 0:45 1:00 1:15 1:30 1:45 Duration of measurement, h:min change. Without bottles, temp increased Medium Density Mixed Load Without Bottles up to 1.2 C higher 9 8 7 False Alarm Alert: Temperature Monitor 6 (vial - floor) Temperature, °C 10 (in box) 6 11 (in box) Placement Matters! 12 (vial - mid) 5 13 (vial - mid) 17 (glycol - floor) 4 Sensors in air, attached to walls, or near 18 (glycol - mid) 19 (glycol - top) 3 20 (vial - low) cooling vents show temperature spikes 2 > 8 °C in all refrigerator types 1 0:00 0:15 0:30 0:45 1:00 1:15 1:30 1:45 Duration of measurement, h:min
III. Power outage Refrigerator type Time after power off until vial temp > 8 °C FREEZERLESS 1.5 to 4.5 hours DUAL ZONE 1.25 to 4.75 hours PHARMACEUTICAL 0.75 to 2.25 hours DORM-STYLE 0.75 to 3.5 hours Freezerless refrigerator – power off trial Vials that resisted thermal excursions 12 1 (top wall) 2 (mid wall) during an outage the longest were: 3 (bottom wall) 4 (top back wall) 10 5 (air) – Contained in boxes, trays, and/or 6 (vial - floor) 7 (air) original packaging Temperature, °C 8 8 (air) 9 (air - top) – Placed away from the top 10 (in box) 11 (in box) 6 refrigerator shelf 12 (vial - mid) 13 (vial - mid) 14 (inside tray) – In a fridge with a water bottle 15 (back of tray) 4 17 (glycol - floor) “temperature ballast” 18 (glycol - mid) 19 (glycol - top) 2 20 (vial - low) LA (floor) Allow 6 to 9 hrs for thermal re-equilibration LC (mid) LD (glycol - top) following an outage 0 0:00 0:30 1:00 1:30 2:00 2:30 3:00 3:30 4:00 4:30 5:00 Time elapsed since power off, h:min
IV. Defrost cycle FREEZERLESS DORM-STYLE DUAL ZONE PHARMACEUTICAL • Defrost cycle runs • Defrost cycle runs at every 2-3 days ~30 h intervals • No defrost cycle • No defrost cycle • Vials occasionally • Vial temperatures • Refrigerator interior exceeded 8 °C for <15 increased ~0.5 °C, did quickly becomes min not exceed 8 °C encased in frost and • Thermometers in air / ice • Some sensors in air / near walls recorded near walls recorded dramatic temperature temperatures > 8 °C spike followed by a for 10-20 min, followed drop below 2 °C by a drop below 2 °C for <10 min Continuous Temperature Monitoring 17 1 (top wall) 2 (mid wall) Vital to proper vaccine storage • 3 (bottom wall) 4 (top back wall) 14 Current “manual check” system: • 5 (air) 6 (vial - floor) • Possible false alarm if checked during 7 (air) 11 8 (air) defrost cycle Temperature, °C 9 (air - top) 10 (in box) • Failure to recognize existence of defrost 11 (in box) 8 12 (vial - mid) cycle and take any necessary protective 13 (vial - mid) measures 14 (inside tray) 15 (back of tray) 5 Freezerless fridge example • 17 (glycol - floor) 18 (glycol - mid) • Cumulative effect of time above 8 °C during 19 (glycol - top) 2 20 (vial - low) multiple defrost cycles? LA (floor) LC (mid) • Evaluate on case-by-case basis LD (glycol - top) -1 Monitor placement is very important! 0:00 0:15 0:30 0:45 1:00 • Duration of measurement, h:min
Vaccine Vial Storage Methods and Locations DUAL ZONE PHARMACEUTICAL FREEZERLESS Never place vials directly on Avoid storing on top shelf – near cooling vent. First location to exceed glass shelf = 2 - 5 °C colder max allowed temp during outages. No storage in vegetable Manufacturer recommends 1 – 2 °C colder crisper: thermally isolated no floor storage, but vial TC than main + floor level runs cold maintained at 2 – 8 °C fridge space throughout testing Best storage practice – place vaccines in center fridge space, contained in original packaging, cardboard boxes, and/or plastic trays to minimize thermal excursions
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