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  1. John Lloyd
  2. équipement de la chaîne du froid
  3. dimanche 3 décembre 2017

Three years after the freeze-free concept was reported at the September 2014 meeting of the WHO PQS Committee, the current expectation of availability remains ‘sometime next year’ and it appears that no product has passed the pre-qualification (E004/VC02-VP.1) testing yet.

The current status of this product was presented at the last Technet Conference by WHO/PQS. During the resulting discussion, I noted five issues that seem to require attention:

  • The outside dimensions and weight of the current prototype products are greater than the carriers used for forty years. We should see comparative data on dimensions, weight of the new and existing carriers because health workers will carry them, often for long distances. Evidence that the increased weight and bulk is operationally feasible should be confirmed by field testing.
  • Freeze-protection in current carrier designs employs a built-in thermal buffer between icepacks and vaccines. The vaccine carrier including the thermal buffer begins the PQS test at +43C when the vaccine load is added at +5C. Evidence was not shared at the Technet meeting that in fact the new products can cool down the test load to below +10C within 8 hours and what is the maximum temperature during cool down?
  • WHO mentioned, in the context of fixed thermostat refrigerators, that replacement of existing equipment by new models will proceed at a ‘natural’ replacement rate under GAVI CCEOP. If this method of replacement is also followed for vaccine carriers that often survive for 10 years, the renewal process will be too slow to avoid a considerable rate of freezing damage.
  • One question raised at Technet has been raised without a satisfactory answer many times in the last 3 years: “Why is the freeze-free carrier the only solution pursued by global stakeholders”. For example, freezers that deliver their frozen icepacks at a few degrees below zero instead of -20C are feasible, but not explored. Phase change materials as a substitute for water/icepacks have been rejected by PQS without clear evidence.
  • The current PQS focus on passive cooling vaccine carriers with icepacks is likely to be overtaken by active-cooled solutions based on adsorption or thermoelectric technology. This solution, in the form of Global Good’s ‘Indigo’ product, gives outreach teams 5 days or more autonomy and streamlines the process of daily short range activities by switching cooling on and off. In spite of these benefits the product has no specification nor pre-qualification test in PQS because it is an active cooler, not passive. The current process for establishing a new product is said to be more than two years.

These questions among others reveal a weakness in the way that the global immunization community handles technology changes for immunization services. Innovation and optimization are treated as ‘solutions hunting for a problem’ instead of operational challenges to the development and growth of immunization – that call for new or improved technologies. Your opinions on how WHO/PQS might strengthen and accelerate this process will be, i I am sure, very welcome !

Mohammad Hamidul Islam Réponse acceptée

This is a request for information  and not a comment. 

Currently we are using ordinary Vaccine Carriers with conditioned ice packs for vaccination at outreach sites. Vaccines have VVM as usual. System works well.

We want to  test  Long Range Vaccine Carriers  with Cool Pack  for the same out reach sites to  see if  that works well. How this pilot study should be done.? Any previous expereince? Can we use the VVM as the only tool in this study to keep things simple.?

Hamidul Islam


Larry Schlussler Réponse acceptée

Conditioned ice packs contain ice and a small quantity of water, these packs are at 0C. If vaccines are placed in a well insluated carrier sourrounded by 0C ice packs the temperature of the vaccines  could easily go below 2C. On a cool morning, the temperature of the vaccines will be even closer to the temperature of the conditioned ice packs. Vaccines do not freeze till temperatures are a little below 0C. I suspect that large quantities of vaccines have been safely transported in carriers where the temperature dipped below 2C while being sourrounded by 0C conditioned ice packs Perhaps the 2C temperature limit should be reconsidered!

John, in the field tests you suggest, would the carrier loaded at 4pm be the new PQS carrier or a standard carrier applying the " Sun Frost No Cost Technique"?

If the morning temperature simulated cool conditions, it would more accurately simulate worst case conditions.


Sun Frost


John Lloyd Réponse acceptée

Good news Isaac! A 'freeze-free' vaccine carrier product has passed the pre-qualification testing - and it does not weigh more than the current carriers; I hope the next step is to conduct some field testing of the new product along the lines of the above discussion:

  • load icepacks frozen to -20C load at 4pm in ambient temp. +/- 30C. The next morning at 7am the inside of the carrier should be at +2C/+8C, ready for risk-free loading of vaccine?
  • load icepacks frozen to -20C load at 7am in ambient temp. +/- 30C. If carrier vaccine space drops below +2C, wait until temperature rises to+2C, then load the vaccine.

The information that managers need for this operational procedure or any other existing practice should answer two vital questions: 1) does this current practice avoid exposure of vaccines to below +2, Yes?No; and 2)  If the answer to 1) is 'No', then how long should we wait in the morning before loading the new carrier with vaccines?

My concern is that several variables affect whether or not the 'freeze-free' mechanism actually protects vaccine from exposure to freezing temperatures. They include the ambient temperature, the temperature of the frozen packs, the amount of vaccine loaded, the temperature of the vaccines at the time of loading. Since this is a passive cooling system there cannot be a thermostat to compensate for differences in these values. Two solutions may exist in the near future:

  • to use active cooling with thermostat or
  • control the freezing temperature to a warmer value

I am confident that we are on the right track to solve these issues - Isaac, it is reassuring about tthe arrival and testing of active portable coolers.

Larry Schlussler Réponse acceptée

Hi Serge,

We are in trouble if the obstcale to eliminating frozen vaccines is not being able to have the staff load the vaccine carriers at the end of the working day.

John pointed that in many facilities ice packs are at -20 deg C. In previous discussions, Umit pointed out that it is difficult to condition ice packs when you have to leave early in the morning. Your situation is apparently different are you talking about a remote facility with solar powered refrigerators?


Sun Frost

Isaac Gobina Réponse acceptée

Hi John – Thank you for your thoughtful post. I’m providing information that I hope the TechNet community finds informative.

Firstly, I am happy to announce that the first freeze-prevention carrier has passed PQS independent lab testing (including the cool down test) and will be published in the coming days. The PQS upper weight limit specification is the same for the non-freeze free and the freeze-free carriers, so no additional weight allowance was provided to freeze-free carriers.

With regard to your comment that the cold chain community is only focused on specific technologies, I want to clarify that PQS is supportive of, and actively seeking innovations that will contribute to solving cold chain challenges in the field that improves the performance, quality, and safety of cold chain technologies. As you know, careful evaluation of performance trade-offs and potential risks is needed when introducing new technology solutions.

For example, engineered phase change materials (PCMs) have been a topic of interest for perceived benefits in reducing the risk of vaccines being exposed to freezing temperatures. The PQS working group has reviewed material compatibility data and consulted UNICEF and EPI teams in order to understand the benefits and risks of allowing PCM into various classes of equipment. After this review PQS has decided to allow PCM in stationary and portable applications where the PCM is not intended to be removed by users. User removable PCM packs are not permitted at this time. The rationale for the restriction on user-removable PCM packs is too lengthy to address here, but some of the key issues are fatty ester PCM incompatibility with high-impact polystyrene (used in vaccine carriers), PCM migration through plastic containers, and that if PCM packs were accidentally placed in a freezer they would still pose a risk of freezing to vaccines. Some of the research PQS used to inform its decision was posted to TechNet and can be found here: Phase-Change Materials for Vaccine Cold Chain Applications.

Finally, PQS has drafted and submitted for industry comment a specification for actively cooled, portable CCE which is where a product such as Indigo would apply. The value proposition for this category of equipment still needs to be informed by field studies of relevant technology and PQS welcomes feedback from all stakeholders (e.g. equipment producers, country health staff) to help inform the final specification.

I hope these points helped clarify the questions raised in your post.

Serge Ganivet Réponse acceptée

Hi Larry,

It looks quite simple at no cost but not sure if really feasible.

From my experience, in most facilities, the staff in charge of immunization leave the facility before 04pm and I do not think they will be willing to load the vaccine carrier with frozen packs for the next day. Also, in many facilities, the water packs are ''frozen'' during the night. During the day the coolant packs are used for the fix or outreach immunization sessions and replaced in the ''freezer'' compartment in the afternoon. Most of the water packs are not ''frozen'' even if there are back-up packs because of small freezer capacity or poor water packs management. But I am interested to hear more about experiences on this issue ''freezing preventive measures''


Larry Schlussler Réponse acceptée

Hi John

I suggested an easily testable solution to the freeze problem in TechNet, however I didn't get any feedback. The thrust of the suggestion is to load the ice packs along with a thermometer in a carrier the night before a trip. The next morning little or no conditioning will be required.

This technique will also make it easier to have an early departure, since little or no conditioning will be required in the morning.

This no cost solution could easily be verified.

Larry Schlussler

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