1. Michelle Seidel
  2. équipement de la chaîne du froid
  3. mardi 28 mai 2019

Dear TechNet-21 Community,

Following the WHO PQS statement on the Vestfrost investigation, please find attached guidance on the management of the equipment and vaccines. Thank you.

Michelle Seidel

Immunization Supply Chain, Programme Division Office: +45 45 33 56 12, Mobile : +45 30 78 76 54, E-mail: mseidel@unicef.org 

United Nations Children’s Fund UN City,Marmovej 51,Copenhagen, Denmark

Follow us on Facebook, Twitter, YouTube and at www.unicef.org 

Pièces jointes
  1. http://apps.who.int/immunization_standards/vaccine_quality/pqs_catalogue/LinkPDF.aspx?UniqueID=5a4cd0be-1468-499b-88e6-b3a226d17e50&TipoDoc=PQS_x0020_Document_x0020_Type&GuidDoc=133bd3e3-99d6-40b9-b6d0-5e653b15e80b
  2. https://www.who.int/immunization/documents/financing/who_ivb_15.04
Larry Schlussler Réponse acceptée


in my last reply it should of read- The NO was left out.


Currently in the field the performance is determined by an alarm system, these alarms have little corrolation to the performance of a refrigerator. In the example given the alarm may have gone off 30 times and yet there were  NO  adverse effects to the vaccines. When the day/night PQS tests are done the performance of the refrigerators is not determined by the currently used alarm systems but by the MKT temperature.



Larry Schlussler Réponse acceptée

Hi Jesse

 As you mentioned you could determine the loss of life of a vaccine from the VVM or its MKT temperature history. When looking at the performance of a refrigerator it is easier to use some method based on the temperature history of the refrigerator rather than looking at the change in dot density of a VVM on a particular vial of vaccine. Based on the refrigerators MKT temperature, the performance of a refrigerator can easily be determined. For example if for a one month period the MKT temperature stayed between 2 Deg C and  8 Deg  C  the life of the life of  vaccines  would not be adversly effected. It may be that during this one month period there were daily temperature excursions to 12 Deg C however the MKT temperature could still remain below  8 Deg C and the vaccines would not be adversely effected.

Currently in the field the performance is determined by an alarm system, these alarms have little corrolation to the performance of a refrigerator. In the example given the alarm may have gone off 30 times and yet there were adverse effects to the vaccines. When the day/night tests are done the performance of the refrigerators is not determined by the currently used alarm systems but by the MKT temperature.

A small electronic device could easily be built which would directly read the MKT temperature. The device could also read out the loss of life of vaccines of different sensitivities. This device would be of paticular value when determining the performance of a vaccine carrier. For example trips could be extened if some percent loss of life on the journey was acceptable. If for example a vaccine was to be used no longer than several days after its arrival perhaps a 50% loss of life would be acceptable.

For a particular vaccine carrier data  could be presented to show how long a journey could be made for a particular % loss of life. This data could be generated during PQS testing, an appropriate test temperature may be 32 Deg C.


Sun Frost


Jesse Ross Réponse acceptée

Dear Rafael,

Manufacturers routinely do accelerated degradation tests at elevated temperatures to determine how temperature-stable their vaccines are.

The results of these tests could in principle be used to enable a direct calculation of MKT on a per-vaccine basis. But more practically and directly, they are used to assign a VVM type to the vaccine. The VVM then essentially does the MKT calculations for us (cf. this document from TempTime for a bit more detail).

Best wishes,

Jesse Ross


Dear Denise

In the table 4 of the document referred by you: "The Use of Mean Kinetic Temperature (MKT) in the Handling, Storage, and Distribution of Temperature Sensitive Pharmaceuticals" wrote by Robert h. Seevers, Ph. d., Jeffrey Hofer, & Paul Harber Eli Lilly and Company https://docplayer.net/355598-The-use-of-mean-kinetic-temperature-mkt-in-the-handling-storage-and-distribution-of-temperature-sensitive-pharmaceuticals.html, we can see that the impact of adding two excursions, each with a temperature rise of 20ºC, each lasting 48 hour the raise is only 1.9° C, from 5.0°C to 6.9°C. 

A conclusion wrote in page 15 was: "it is incumbent on manufacturers (of vaccines) to perform the necessary stability studies so that the MKT of a temperature excursion can be compared against available stability data to enable an informed conclusion regarding the impact on product quality"

Would be good have MKT specific for vaccines, because those studies are for pharmaceutical products.

Best regards.

Larry Schlussler Réponse acceptée

Hi Denise

Thank you for the clarification on PQS allowed temperature swings. Previously no temperatures swings below 2 Deg C were allowed. I also received a clarification from Isaac.

For the day/night temperature tests MKT temperature is used to acess the cumulative effect of temperature excursions. I think it  would also be benefical to assess the effect of temperature excursions in the stable run tests using MKT temperatures. If for example each night the temperature went to 12 Deg C for two hours,  the MKT temperature could still be below 2 Deg C  and the life of the vaccine would be uneffected. Having temperature limits which are unnecessarly restricitive at one end of the temperature scale may make it difficult for manufactures to meet the temperature requirments at  the other end of the temperature scale.


Sun Frost


Denise Réponse acceptée

Dear Larry, 


Have you reviewed the WHO PQS testing protocols for fridges and freezers on the PQS website? I have shared a couple of protocol links and attachments for ease of reference: 

PQS testing protocols list criterias for qualification, including acceptable temperature ranges that are defined as follows:

Acceptable temperature range: The acceptable temperature range for storing vaccine is +2°C to +8°C. However, transient excursions outside this range will be tolerated, within the following limits:

  • No excursion must exceed +20°C (± 0.5°C) for any amount of time.
  • No excursion must drop below -0.5°C for any amount of time.
  • No excursion must drop below 0°C for longer than 1 hour.
  • Following an excursion below 0°C, the appliance must return to safe operating temperature (i.e., consistently between +2°C and +8°C) within 2 hours. This duration will be measured from the moment the temperature drops below 0°C and up until it returns to +2°C.

The cumulative effect of any excursions within the above range will be assessed over the five day period of the day/night test. For this test, the calculated mean kinetic temperature (MKT) must remain within the range +2°C to +8°C when the default activation energy is set at 83,144 kJ per mol. Using the recorded temperature data, an MKT figure will be calculated for each sensor. The worst-case result will determine the outcome of the test. Excursions in other tests will be noted and must not exceed the defined upper and lower limits.

I hope this helped answer your questions!

Best wishes,


Pièces jointes
Larry Schlussler Réponse acceptée

Hi Michelle

I realize that freezing is not allowed in the refrigerator compartment. What I was asking was what exactly the PQS  test standards are; are certain temporary excursions below 2 deg C allowed during a PQS test.


Sun Frost




Michelle Seidel Réponse acceptée

Dear Ian,

Not all Vestfrost Equipment has been delisted- please find the affected models  here.

No Haier products have been withdrawn from PQS due to performance or quality complaints.

Dear Larry,

Freezing is not acceptable in the refrigeration compartment, obviously in the freezer this is acceptable.


ian.tansley Réponse acceptée

Hi Larry

My understanding is that ALL Vestfrost refrigerators have been struck off the WHO PQS list as a result of the discovery of frequent freezing conditions in the refrigerator compartment. 

Did I hear someone say that some Haier product has also been de-listed?


Larry Schlussler Réponse acceptée

After reading the WHO statement I was not clear on exactly what the PQS standards are:

does the refrigerator have to stay between 2 deg C and 8 deg C or is the the freezer allowed

to go to -5 deg  C for less than 1 hour. Could some one please clarify.

Carlton Banks Réponse acceptée

Dear Rafael,

WHO have posted further information on their PQS website providing user guidance and informing the applicable Vestfrost products have been suspended from the PQS list pending their investigation.



  1. https://apps.who.int/immunization_standards/vaccine_quality/pqs_catalogue/LinkPDF.aspx?UniqueID=5a4cd0be-1468-499b-88e6-b3a226d17e50&TipoDoc=PQS_x0020_Document_x0020_Type&GuidDoc=478c2315-94b4-4eeb-afd5-2dcc1bfb93ae
  2. https://apps.who.int/immunization_standards/vaccine_quality/pqs_catalogue/LinkPDF.aspx?UniqueID=5a4cd0be-1468-499b-88e6-b3a226d17e50&TipoDoc=PQS_x0020_Document_x0020_Type&GuidDoc=eff43e2d-f512-4ada-88d9-aa770a2be132
Michelle Seidel Réponse acceptée

Dear Rafael,


Thank you for the information.

Vestfrost has submitted a report to PQS. Their findings are currently being independently verified. PQS should have an update soon. 


Dear Michelle

Has Vestfrost given the explanation about that situation? In Colombia we have those equipments working well (ILR and SDD). 

Best regards

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