The dosage of the mumps vaccine component in MMR is the same as of Mumpsvax, "Each 0.5 mL dose contains not less than 20,000 TCID50 (50% Tissue Culture Infective Dose) of mumps virus." The Merck product information recommends MMR as the secondary vaccination treatment with Mumpsvax.
Mumpsvax is produced from the Jeryl Lynn strain of mumps virus developed by Maurice Hilleman. When his daughter Jeryl Lynn Hilleman contracted Mumps (in 1963) Dr. Hilleman cultured the vaccine strain from her throat. The mumps virus strains were developed in embryonic hens' eggs and chick embryo cell cultures. The resulting strains of virus were less well-suited for human cells, and are thus said to be attenuated. They are sometimes referred to as neuroattenuated in the sense that these strains are less virulent to human neurons than the wild strains.
The cells used in culture, virus stocks used, and animal fluids are all screened for extraneous material as part of the vaccine production. They are grown in Medium 199 (a solution containing buffered salt, vitamins, amino acids, fetal bovine serum) with SPGA(sucrose, phosphate, glutamate, human serum albumin) and neomycin. The human albumin processing uses the Cohn cold ethanol fractionation method.