Safety of the cold chain
If vaccines are spoiled by incorrect storage conditions, they will not be effective in preventing the associated disease, and they could also cause adverse reactions. This is also true for the diluents (ampoules of special liquid) used to reconstitute the freeze-dried (powder) BCG and measles vaccines before use. Each of these vaccines has its own specific diluent, which cannot be used for another vaccine. Diluents can be stored at room temperature if there is no room for them in the refrigerator, but before use they must be completely chilled to between +2oC and +8oC, so they reach the same temperature as the vaccine they are being mixed with.