Background and Aims: The safe, potent and effective live vaccines against Measles, Mumps and Rubella as important childhood diseases have been available for several decades. Several factors can affect the thermal stability of lyophilized vaccine.

Methods: In this study, the effect of residual moisture on thermal stability of 61 batches of MMR vaccine was investigated using an accelerated method that has been recommended by World Health Organization (WHO).

Results: Our results suggest that the best thermal stability for the lyophilized MMR vaccine is in a range of 1.51 to 2.00% of residual moisture with the minimum decrease in the all three components of the vaccines.

Conclusion: It is suggested that the lyophilizators of MMR vaccine production lines should be programmed in a manner that the best range of residual moisture achieves.