POST 01058E : ORAL POLIO VACCINE COLOUR
Follow-up on Post 01050E
25 February 2007
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Hans Everts (mailto:[email protected]) from WHO replies to Jedeth
Mamora's question on OPV colour.
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As a response to the message from Jedeth Mamora in Indonesia first a
small but important correction. The VVM does not measure
effectiveness of the vaccine, but heat exposure. That is not just a
matter of semantics. A clearly polluted vial with a good VVM should
not be used. Heat exposure is only one of several components that
contribute to the loss of potency.
The issue of coloured OPV was submitted to a technical colleague,
Jackie Fournier-Caruana, here at WHO some time ago. Her response was
the following:
The pink color of OPV (either tOPV or mOPV) is given by the presence
of phenol red used as pH indicator. This reagent is a residual
product from the vaccine production on cells but can also be added at
the time of the formulation. Its pH range is from 6.4 to 8 and its
color varies from yellow at pH 6.4 to red at pH 8.
In the past, WHO received similar complaints from the fields for tOPV
produced by different manufacturers and more often for vaccine
presented in plastic dispenser than in glass vial. Further to
investigation conducted at that time in conjunction with
manufacturers, it was concluded that the slight variation of pH
leading to the change of colour could be due to exposure to
evaporating dry ice and production of CO2. However, the potency and
efficacy of the vaccine are not affected by this change of pH,
provided that the range of 6.5-7.2 be respected, corresponding to a
color varying from yellow to pink red. Similar observations were made
by Mauler and Gruschkau who studied monovalent polio vaccines with pH
values ranging from 5.5 to 8.0. They concluded that polio vaccines
were remarkably stable within the pH range 6.5-7.2. Reference to
their original article (Mauler R, Gruschkau H. : "On stability of
oral poliovirus vaccines". Developments in biological
standardization, 1978, 41: 267-270) was included in the document
"Thermostability of vaccines (WHO/GPV/98.07. )" . But this article is
no longer available and the WHO document has now been replaced by a
revised version "Temperature sensitivity of vaccines (WHO/IVB/06.10)"
in which the reference does not appear anymore.
The conclusion is that the change of the colour does not invalidate
the VVM reading.
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