Experience thus far with use of Controlled Temperature Chain (CTC) vaccines indicates that a longer CTC duration may be more important than CTC qualification at a high temperature (e.g., above 40°C). Therefore, WHO currently recommends that vaccine manufacturers conduct CTC stability tests at both 37°C and 40°C and seek to extend the CTC duration for as many days as data supports beyond the current minimum of 3 days. Manufacturers should also engage in dialogue with WHO before stability testing for CTC qualification to discuss the programmatic need for CTC use of the particular vaccine, suitability of the test protocol, and minimum acceptable potency level for regulatory and WHO prequalification approvals. Manufacturers should also contact WHO after stability testing for CTC qualification to discuss the results and confirm labelling plans for the product insert prior to regulatory and WHO prequalification approvals.