POST 00569E : FREEZING OF SINGLE-DOSE VACCINE PRESENTATIONS
Follow-up on POST 00568E
5 June 2003
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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.
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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
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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
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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.
Claude Letarte
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