POST 00501E : CHILLED WATER PACKS STUDY
Follow-up on Posts 00485E
15 September 2002
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Sam Kamau (mailto:[log in to unmask]) from Kenya expresses some
concerns about chilled waterpacks followed by comments by Michel Zaffran
(mailto:[log in to unmask]) from WHO about keeping vaccines in holes of foam
pads.
I have put both these comments under "Chilled Water Packs" although
Michel's contribution isn't directly related. The "More Cold-Sensitive
Vaccines" issue was really about protecting some vaccines from freezing
that is not normally the issue for reconstituted measles.
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I am rather concerned to read this article concerning the use of cool or
wet icepack during the measles administration after the reconstitution .
The health workers know that reconstituted measles and BCG should always be
kept on a frozen icepack for the six hours.
The the issue of monitoring the six hours duration is also very critical.
The issue of using cool or wet icepack will definitely waterdown the
importance of the health workers sensitivity to the use of the frozen
icepacks in the overall vaccine management and should not be discussed in
any forum.
Sam Kamau
National EPI Logistician
Kenya
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The use of the foam pad and putting vials of vaccines in the holes of the
foam pad was an approach promoted 10 years ago to avoid that icepacks be
removed from the vaccine carrier thus substantially reducing its cold life
and all potentially jeopardizing the other vials inside the carrier
If ice or additional icepacks are available then they should be used to
keep the open vials cold (these would be in addition to those needed to
keep the vaccine carrier cold : i.e. the full load of icepacks recommended
by the manufacturer for the expected cold life of the carrier).
However if one has to choose between keeping the vial in the foam pad or
removing one of the icepacks from the carrier and putting it on the table
to keep the open vial cold, then I believe the foam pad is a better choice
Michel
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Moderator's comments :
It is true that policy changes may generate some confusion. However at this
point I wish to stress that no such change has occurred. It should also be
clear that if and when chilled waterpacks are approved by a revised WHO
policy document this would apply only for vaccine transportation.
Reconstituted vaccines such as measles for example, have to be kept within
a temperature range of 2° to 8°C for a maximum of 6 hours.
I also wish to use this opportunity to put my own questions forward to the
Technet audience. I wonder if other members have had similar thoughts. And
this is about the diluent. I have shared the accepted truths so far.
However I have been puzzled lately to the point of doubting these truths.
And I wish to have your comments and hopefully some answers that I haven't
found to my satisfaction yet.
Even before publishing the posting in which the temperature of the diluent
was discussed (Post 00494E), I had questions when consulting the
manufacturer's notice of measles in North America (marketed as MMR but each
component is produced separately). It is recommended that the diluent be
kept at room temperature to save cooling space in the refrigerators and it
doesn't require that it be cooled before reconstitution.
I further discussed with a scientist working at the manufacturer. They
maintain that a warm diluent even at 43°C cannot harm the virus, the
so-called "thermal shock" to the vaccine is not known and the diluent
should be kept and used at ambient temperature as per their recommendation.
But incubation does harm the virus and reconstituted measles vaccine has to
be kept cool at 2°-8°C. This tends to confirm the principles of virus
biology and what happens to a live virus in a vaccine solution, although I
admit these principles I acquired a while ago. There are few absolutes in
science and as we all know scientific truths change sometimes.
I got also puzzled by the interpretation we probably all made of the part
of the article posted in POST 00494E. If the diluent was prewarmed at 41°C
and then incubated at that same temperature, how can we scientifically draw
the conclusion that the warm diluent harmed the virus as compared to the
incubation?
In the meantime I came upon another article that had been published on the
same topic before the one referred to in the posting (Peetermans J, Colinet
G, Stephenne J, Bouillet A., "Stability of freeze-dried and reconstituted
measles vaccines", Dev. Biol. Stand. 1978;41:259-64). It had concluded
differently that "Reconstitution with diluent at 41° C and subsequent
exposure to this temperature does not affect the titer significantly during
the first half hour."
So where is the truth? Is it that titers were measured with different
methods? Can this differ depending on the manufacturer?
So I leave it to you all to bring some further light on this point. I admit
to my own confusion.
Claude Letarte
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