Interference between strains in live virus vaccines, I: Combined vaccination with measles, mumps and rubella vaccine.

One to four different lots of four commercially available trivalent measles-mumps-rubella vaccines were tested for their efficacy as measured by the induction of antibodies to the three vaccine viruses. All of the products were satisfactory although a 100% seroconversion rate was attained regularly only with rubella vaccine. The live virus in the different measles and mumps vaccine components and especially the relative amounts of measles to mumps virus varied widely. Obviously, the efficacy of a vaccine should not be judged only by the virus content. Of main importance is the further adjustment of the dosage of the interfering vaccine virus strains in relation to their attenuation.