Improvement in potency assay of measles-mumps-rubella trivalent vaccine: interference between components and measures for its elimination.

In the potency assay of trivalent measles-mumps-rubella (MMR) vaccine by the immunocytochemical focus assay reported previously (Fukuda et al., 1987), development of rubella foci in RK13 cells was inhibited in the presence of a large excess of mumps component, resulting in an underestimation of the titre of the rubella component. When RK13 cells are infected with the mixture of mumps and rubella viruses, mumps virus interfered with the growth of rubella virus. Interference was mediated most likely by interferon induced by mumps virus. The interference was eliminated by a partial neutralization of mumps component by the addition of anti-mumps serum to the inoculum to RK13 cells. Improved method of potency assay of MMR vaccine incorporating the above measures and other modifications are described.