The purpose of this study was to add to the body of evidence that is being generated to determine whether new policies and guidelines can be developped on the use and storage of vaccines at higher temperatures than the traditional 2-8°C , but still under controlled conditions. Such guidelines have not so far been issued by WHO but work is underway and is being discussed by the WHO Technology and Logistics Advisory Committee (TLAC). Several countries however have already initiated strategies which take vaccines such as Hepatitis B beyond the existing cold chain to increase outreach for the delivery of the birth dose.
To specically address your question, the correlation between the potency of OPV and the VVM reading has been studied by the NIBSC in the UK aat the request of WHO. The report of this study was published under the reference WHO/V&B/99.11 (
http://whqlibdoc.who.int/hq/1999/WHO_V&B_99.11.pdf)
regards
Michel Zaffran