Friday, 12 February 2016
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Immunization outreach services depend on a protective, affordable and efficient supply chain to benefit rather than obstruct outreach operations. Four potential cold-chain solutions are on offer but each has barriers to be negotiated or removed. The options are:

  • Frozen water packs BUT we should switch to freeze-free vaccine carriers to avoid the risk of freezing:
  • Vaccines certified for use in a ‘Controlled Temperature Chain’:
  • PCM-filled packs used in all existing carriers and boxes prevent freezing BUT pending resolution of cost and other issues by WHO.

So, which of the 3 solutions interests you most? Do you know of others? I await your views and look forward to a lively discussion!

(See the attachment!)

8 years ago

I don’t see how a PCM would protect a vaccine from freezing. PCM filled packs freeze at temperatures above 0°C. If they are left in a freezer which is below 0°C the pack will go below 0°C and will be able to freeze vaccines. For example, a PCM which melts at 4°C could be stored in a -15°C freezer. The pack will then be at -15°C when removed from the freezer and will be capable of freezing a vaccine. When the packs warm to 4°C they will begin to melt; as with frozen water packs, if PCM packs are not conditioned they could freeze a vaccine.

On an excursion an MKT thermometer would be a simple way of seeing the effect of temperature variations on the life of a vaccine. A single number would tell you the percent loss of life on a trip. See our previous posts on tech net for more details.

An additional aid in vaccine distribution may be a “buffered temperature chain,” discussed in a previous post. This relies on simple strategies such as evaporation to protect a vaccine from high temperatures. Use in combination with an MKT thermometer, the effect of temperature variations on a trip could easily be evaluated.

I think that freeze-free vaccine carriers would have a significant impact on protecting the vaccines. The process of conditioning the icepacks or de-freezing before use is not always followed. Perhaps the problem is that it is not an absolutely clear and objective criterion. It is not easy to know exactly what time the icepacks will be needed and to make sure they are at the right temperature for that point in time. But replacing current vaccine carriers with freeze-free units would be a long and costly process.

In the mean time how about some research towards identifying effective insulating materials that could be used as an extra lining in the current vaccine carriers between the icepacks and the vaccines like a small bag. That could be a relatively cheap solution and could be used when the vaccine carrier is loaded…. Just a thought.

PCM-packs would not help solve the freezing issue. The vaccine supply chain is already equipped with water packs and health staff is used to the conditioning (freezing) of the water packs. Replacing water-packs with PCM-packs would be costly and I am not sure the benefit of faster conditioning and longer lasting cooling would justify the investment.

8 years ago

Dear Claire and Larry!

Yes, I believe that the common consensus is that compliance with the icepack pre-conditioning procedure recommended by WHO is too low to be useful. This leaves only two, passive cooling options. Either we use water-icepacks (not water alone for outreach) that are prevented from freezing the vaccine load.. Or we use PCM packs that never reach zero degrees:

  • The ‘freeze-free’ passive carrier prevents freezing by using a jacket (not a bag) to separate vaccines and water-icepacks; so, your solution really
  • The PCM packs do not require a freezer to solidify – a couple of degrees difference will do the trick over night and a day. So – 4 packs being solidified in a refrigerator are swopped with 4 packs taken for use.

But yes, we don’t yet know the overall cost of the water-icepack solution v. the PCM pack solution – we need this information and we wait for an alternative, active cooling option for carrying vaccines!

Dear James!

I like your point very much and I see two ways to interpret what we should do to address it! The first is managerial: as we see outreach immunization operations grow, an increasing burden is placed on health workers who are often already occupied with fixed sessions, we should focus on micro-planning to deploy staff, budgets and transport - according to a single callendar of activities? Yes?

The second is cc equipment. As Medecins Sans Frontiers lamented at their February meeting in Oslo a year ago, “[The cold-chain has become an obstacle to reaching children in areas of difficult access]”. Cost, weight, bulk and cool-life all need to guide us towards a solution that would be best in each situation, right? If ‘yes’, then we should evaluate these points , then decide on a solution.

8 years ago

Unfortunately I made my comments before I looked at John’s attachment. If the 4°C PCM is frozen in a refrigerator compartment which is at 2°C then no conditioning would be necessary. To safely cool these ice pack sin a refrigerator a compartment would be needed which is thermally isolated from the vaccine storage area. It would not be advisable to place warm PCM packs adjacent to stored vaccines. These isolated compartments are available on very few refrigerators, which is problematic.

If a 4°C PCM is being solidified in a compartment which is at 2°C then the freezing process would be very slow. Perhaps some tests have been done to measure the freezing rate

Claire Frija Madsen suggested placing an insulating material between the vaccines and the ice packs to keep vaccines from freezing. This technique will increase the temperature of the vaccine storage area in the carrier. What would be more effective is a layer of water between the sub cooled ice packs and the vaccines. The sub cooled ice packs will then freeze some of the water in the barrier and protect the vaccines from freezing. The thickness of the water layer would depend on the quantity and temperature of the sub cooled ice packs. If the entire layer of water in the barrier does not freeze it is thick enough. With support we could design a simple phase change barrier based on this principle.

After doing some back of the envelope calculations I came to the conclusion that the freezing of vaccines by sub cooled ice packs increases geometrically as the temperature of the ice packs decreases. In other words, an ice pack at -20°C will be 4x more problematic than an ice pack at -10°C.

One simple method to minimize the problem is to set the temperature on the freezer no colder than necessary. For example, if you have 2 days to freeze your ice packs you may be able to set your thermostat to a much warmer setting. This will also save energy and reduce the run time of the compressor. One of the barriers to setting the thermostat warmer than -6°C is that the ice packs will sometimes sub cool, which is to say that they won’t start to freeze until the temperatures of the water pack is close to -5°C. Elimination of sub cooling would allow the temperature of the freezer to be set much closer to 0°C.

We are currently developing an essentially no cost method to accomplish this. Eliminating sub cooling would then allow ice packs to be frozen at a higher temperature which would reduce the risk of freezing vaccines and the time it takes to condition ice packs.

8 years ago
Larry, so very true and thank you for bringing this about. Best Soren Sent from my iPhone Best regards Søren Spanner
8 years ago

Hi John,

I did not understand the first sentence of your Feburary 15th comment. You said "procedure recommended by WHO is too low to be useful". What is too low? Thanks forclarifying.

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