WHO still recommends that single antigen freeze-dried (lyophilized) vaccines and OPV should be distributed in cold boxes or vaccine carriers, lined with frozen icepacks.
Field studies continue to show that vaccine freezing during transport remains one of the principal causes of damage to freeze-sensitive liquid vaccines in the cold chain. The use of ‘conditioned’ icepacks has previously been recommended as the way to avoid this risk; however icepack conditioning is a time-consuming process and recent cold chain surveys have shown that the practice is difficult to enforce and is widely ignored. You should note that the use of cardboard, newspaper or similar material to isolate freeze-sensitive vaccines from fully frozen icepacks is completely ineffective as a means for preventing vaccine freezing..
The only way to eliminate the freezing risk entirely is to transport liquid vaccines, other than OPV, in cold boxes lined with cool water packs which have been pre-cooled in a refrigerator to a temperature of +2°C to +8°C. Where it is essential to transport OPV, liquid and freeze-dried vaccines in a single carrier, experiments have shown that cold water packs may safely be used provided the cool water pack cold life of the carrier is not exceeded. These recommendations are based on the field studies organized/conducted by WHO that was published in PDA Journal of Pharmaceutical Science and Technology, Vol. 63, No. 1, January–February 2009 (Umit Kartoglu, Serge Ganivet, Stephane Guichard, Venkat Aiyer, Peter Bollen, Denis Maire and Birhan Altay). I am attaching this article as a further reference (This study was awarded by International Quality and Productivity Centre IQPC Best Logistics Project European Awards 2010 in Amsterdam, the Netherlands). Again, based on this article, "cool chain" was defined by the PQS (Performance, Quality and Safety) project and incorporated into E04 and E05 product sections. Cool life is defined as follows: "The empty container is stabilized at +43°C and loaded with coolpacks which have been stabilized at + 5°C for a minimum of 24 hours. Cool life is measured from the moment when the container is closed, until the temperature of the warmest point inside the vaccine storage compartment first reaches +20°C, at a constant ambient temperature of +43°C." The following documents could be viewed for more detailed information:
http://www.who.int/immunization_standards/vaccine_quality/pqs_e004_cb01_2_pps.pdf
http://www.who.int/immunization_standards/vaccine_quality/pqs_e004_vc01_2_pps.pdf
PQS Guidance notes that will be available in a short time along with the launch of new PQS Database recommends the use of either 3 packs for vaccine transport:
1. Frozen icepacks (for vaccines OPV and single antigen freeze-dried (lyophilized) products)
2. Cool water packs (for all freeze-sensitive vaccines and wherever combination of OPV, single antigen freeze-dried (lyophilized) and freeze-sensitive products need to be carried together in one box)
3. Warm water packs (at extreme cold ambient temperatures for all vaccines)
Along with this, WHO PQS no longer recommends the use of conditioned icepacks.
Changing over to the use of cold water packs involves significant alterations in practice. In addition there are equipment implications because additional refrigerators will be needed at primary and intermediate level to cool the cold water packs in bulk. Consequently it is strongly recommended that the introduction of this method should be preceded by a formal cold chain study as described in WHO/IVB/05.01: WHO Study Protocol for Temperature Monitoring in the Vaccine Cold Chain. designed to establish the extent of current problems and the logistical and financial implications of the changeover.