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  3. Tuesday, 19 October 2010
I have one suggestion on a different topic for which I need comments from experts.  In Polio Eradication programs, the Non-Polio Entero virus rates in the stool specimens is taken as a proxy indicator of adequate stools and effective reverse cold chain. This indicator becomes all the more important in areas which have 0 polio cases. Now there are areas within these regions which show very low NPEV rates casting doubt on the effectiveness of their reverse cold chain. Can we use empty polio vaccine vial with 0 stage VVM in these stool carriers as our monitors of reverse cold chain and their status can be noted by the recieving laboratories? If this is possible, it could be an effective effecient and logical means of monitoring reverse cold chain.  Best regards, Dr. Faisal MansoorSr. Epidemiologist/National Program Manager NICP-Islamabad. Pakistan 
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I think using VVMs to test the reverse cold chain is problematic because: the VVM sensitivity is based on the minimum acceptable titre of the Sabin virus in the OPV. A VVM at stage 3 or 4 means that the OPV titre is close to the minimum level (with a safety margin), but not that there is no more living virus. It would be impossible from that observation to extrapolate to the quality of the stool sample, which may have very different sensitivuty criteria. The receiving laboratory can record the VVM status, but how should it be interpreted, in particular on a case by case basis? The status of the VVM at the receiving point will depend on the status at the starting point. The intention may be to use VVMs at stage 0, but that will be hard to verify if adding an empty vial to every stool sample becomes general practice. Even when there are many SIA it is not rare that VVM are already at stage 2 at the start of the campaign. This is probably worse for routine vaccine due to lower turnover. In addition, we would not want a health centre not to send a sample because there is not empty vial with VVM 0, or to empty a vial to send it with the stools. But more importantly, most reverse cold chains function fine and I do not think a change in general practice is the best solutions for rare events. Such solutions tend to increase the workload disproportionally to the risk, and worse, lead to wrong conclusions.  If there is a reason to suspect a dysfunctional reverse cold chain (for example a low NPENT and Sabin detection rates, no WPV detection in areas bordering areas with intense transmission, or systematic arrival at the laboratory with unfrozen icepacks) I think the best solution is to send some temperature loggers with stools shipped from the suspected region. The loggers allow you to see by how much, for how long and when (where) the temperature was out of range and to address the problem.  There may be many causes of geographical, environmental and seasonal nature for low NPENT rates other than the reverse cold chain.  I hope this helps?
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Thanks for raising the issue. This issue has been addressed by using specially designed temperature monitoring device for the purpose to be used in the stool carrier in case such type of situation arise or in areas with persistantly low EV isolation rates in the stool samples Regards Dr. Hassan Khan Medical Officer (TIP) WHO/Polio Sudan at Nyala +249912360291
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