POST 00569E : FREEZING OF SINGLE-DOSE VACCINE PRESENTATIONS

POST 00569E : FREEZING OF SINGLE-DOSE VACCINE PRESENTATIONS Follow-up on POST 00568E 5 June 2003 ________________________________________________________________ This posting contains two contributions, both questioning the comparisons of freezing time of single-dose versus multiple-dose presentations. The first is from Anil Varshney (mailto:[log in to unmask]) from India. The second is from Andy Tucker (mailto:[log in to unmask]) from PATH. Please note that Anil is asking for suggestions to solve a problem that is not so common in the world but nevertheless very important. I don't think that the type of refrigerator that he imagines ever exists. Such versatility is now common in air conditioning equipment but not for refrigerators. ________________________________________________________________ Good to hear the arguments on single and multidose vial freezing. Well in practice simple logic seems to work which is also the basic principle of physics. The small dose vial will freeze faster than larger dose, but if an equal number of small doses are kept together than they will freeze later and slower than multidose, because they would be occupying more space say 3 -4 times than multi dose. I also want to know the answer for preventing freezing in cold climate in the Himalayas. During my recent visit to Bhutan ( WHO assignment) I found that due to ambient temperatures being low, freezing was common and refrigerators are no good. Further it is impossible to keep the room warm as their is no electricity and burning kerosene stove unattended by staff is fraught with danger. SO WHAT ARE THE OPTIONS? Are there automatic refrigerators that can cool and warm the content or can we think of some thing simpler that would maintain the temperature at 2-8°C , safe enough for most vaccines. Solution to this will save a lot of vaccine that get frozen and thawed without even the knowledge of staff, unless they do shake test. With kind regards Anil Varshney _________________________________________________ Just a technical note of clarification. 20 doses will not take nearly 20 times to freeze as 1 dose does unless the vaccine is stored more like a sphere. Freezing will be based on the surface area of the liquid, so it will depend on the relative proportion of height and radius of the cylindrical vials. One could pull out the old math book or derive the equations from calculus, but suffice it to say that 20 doses will freeze faster than 20 times that of a single dose. Or, one could just study how long it takes for different presentations to lose their potency, which is really our concern. Andy Tucker _________________________________________________ Moderator's note Both are right and it is simple physics. 20 single-dose vials packed together will actually freeze slower than one 20-dose vial. But the ones on the outside may freeze earlier than those inside. This brings us back to the multiple factors that were mentioned in the previous posting. However Andy's comment about "what is our concern" is the most critical. It may be very nice to know how fast various vaccine presentations will freeze. But in practice it is rather irrelevant for vaccine management. Freezing occurs accidentally and unintentionally, not in controlled trials situations. Nobody is going to calculate the time it could take for freezing depending on the volume, the density and molarity of the liquid, the temperature, the energy transfer capacity of the containers and the packaging and so on. In no circumstances should vaccine be exposed to freezing temperatures in storage or transport...period. Because we know that freezing will slowly destroy the vaccine. Again it is physics. Every small organism be bacteria or virus, or proteins like toxoids can be frozen but it needs to be in specific conditions, especially being frozen very fast at very low temperatures in liquid nitrogen (below -100°C I believe) Then it can be lyophilized safely and if kept in tight containers and never exposed to any molecule of water, they can be kept at room temperatures on the shelf for a very long time. Freezing slowly at high temperatures just below the freezing point makes different ice and very unstable crystallization. And the constant reshuffling of crystallization lines will eventually destroy what is being frozen. In the case of vaccines, it is the adjuvant when present that is the very real problem. The adjuvant will cause the vaccine being damaged much faster and is the reason behind floculation that permits the shake test. If I am wrong please someone correct me. 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