Expanded programme on immunization (EPI). Safety of high titre measles vaccines.

Unexpected results suggesting decreased survival when compared with standard titre vaccine administered at 9 months of age have been found in some field studies evaluating the performance of high titre measles vaccine. Analytical difficulties have arisen because the studies were not specifically designed to measure survival. Nonetheless, careful analysis of the results from all of the high titre vaccine trials showed decreased survival of high titre vaccine recipients, in areas with high background mortality rates, compared with recipients of standard measles vaccines at 9 months. No systematic biases could be found in the studies to explain these differences. Statistical analysis of these data suggested that the findings were unlikely to be attributable to chance alone. The panel recommended that high titre measles vaccine derived from the original Edmonston measles vaccine isolate should no longer be recommended for use in immunization programmes. Further post-licensure field studies of new measles vaccines should take into account the results of these studies. Additional detailed epidemiological studies in populations that have received high titre vaccines and their controls were encouraged.