POST 00505E : USE OF VVMs
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POST 00505E : USE OF VVMs
27 September 2002
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Ümit Kartoglu (mailto:
[log in to unmask]) from WHO reacts to previous
comments on the use of VVMs.
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In POST 00480E (29 July 2002) Carib Nelson (PATH) suggested that "since it
(OPV) is the least stable vaccine, it would seem reasonable to assume that
in an outreach box with a mix of vaccines, if the OPV VVM is still OK then
the others vaccines should be OK as well." In POST 00482E (31 July 2002),
Robert Steinglass (BASICS) underlined that "the most heat-sensitive vaccine
is not OPV, but reconstituted measles." In the same posting, Anthony
Battersby suggested a correction to Carib's thinking that "you can only use
OPV as a proxy if all the other vaccines have followed the same cold chain
up to the moment that you wish to use OPV as a proxy."
It is thus necessary to stress the following two points :
1. If vaccines were listed in order of heat sensitivity, OPV would be at
the top of the list followed by measles. This list is based on vaccine
stability tests at 3°C. Whatever their rank in the list however, all
freeze-dried vaccines must be discarded 6 hours after reconstitution or at
the end of the session whichever comes first. For example, BCG is more heat
stable compared to DTP, but it (BCG) has to be discarded 6 hours after its
reconstitution while DTP can still be used in subsequent immunization
sessions in accordance with the multi-dose vial policy. This is also why
VVM on a freeze-dried vaccine is always placed either on top of the cap of
a vial or on the neck of an ampoule.Then it is discarded during the
reconstitution process and cannot be referred to anymore. As for liquid
vaccines (like DTP), VVM is always placed on the label, visible at all
times even after the vial is opened.
2. WHO never recommended the use of one type of VVM as a proxy indicator
for vaccines without VVM. WHO states that "vials with VVMs should NOT be
used as proxy indicators of heat exposure for vials without VVMs. Vials
without VVMs should be handled as they always were." This also applies to
the same type of vaccines that VVM on a vial of OPV cannot be used as proxy
indicator for OPV vials without VVM. What Anthony describes as a condition
for using OPV VVM as a proxy indicator should also be disregarded.
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