Dear sirs,
In the specific case of the Serum Institute laboratory, the package insert states that it is recommended to store the vaccines in the dark, between 2°C and 8°C. For long-term storage, a temperature of -20°C is recommended for the freeze-dried vaccine. The diluent should not be frozen, but kept cool.
The question arises because these BCG and measles vaccines, in combination with rubella and mumps-rubella, arrive at a MKT of around -3°C; that is, they don't reach -20°C, but neither do they reach the 2°C to 8°C range. We store them refrigerated and continue to do so until administration, but I don't know if they can be frozen at -20°C after having been stored between 2°C and 8°C.
Best regards.