A European collaborative study to assess the proficiency of laboratory estimates of potency of live measles, mumps and rubella tri-valent vaccines.

A collaborative study involving 10 European laboratories was undertaken to assess the variability of estimates of the potency of measles, mumps and rubella tri-valent vaccines. The precision of assays as demonstrated by tests on duplicate samples was good; differences averaged around 0.2 log10 steps. Similarly, assay to assay variation within laboratories was small with most achieving consistency around 5% over three assays. In contrast, overall median variations in potency between laboratories were around 1.0 log10 for measles, 3.0 log10 for mumps and 2.0 log10 for rubella. Unexpectedly, the variations in estimates for measles and rubella were not improved when potencies were expressed relative to reference preparations. However, for mumps variability was reduced by using a reference but only for the vaccines of the same strain as the reference. For these Urabe mumps vaccines the variation in relative potency was around 1.5 log10.