Is an improved measles-mumps-rubella vaccine necessary or feasible?

The measles-mumps-rubella (MMR) vaccine has been very effective in the elimination of disease and has high biosafety. However, it has been associated with several adverse effects and has recently caused controversy with regard to its possible association with inflammatory bowel disease and autism. This has been postulated to be a property of the measles component of the vaccine, and a "new variant" autism has recently been described and suggested to be associated with vaccine virus. Although one study has reported the presence of measles RNA in inflammatory bowel disease associated with autism, this has not been independently confirmed. This and most of the other demonstrated or perceived adverse effects of the MMR vaccine could theoretically be ascribed to its composition as a mixture of three live replicating viruses, one of which (measles) can induce immunosuppression, although this hypothesis is speculative. It may nonetheless be desirable to improve the biosafety of the MMR vaccine by the development of a nonreplicating vaccine that will stimulate efficient immunity and protection. DNA vaccines for measles, mumps, and rubella viruses have been constructed and tested in animal models but are poorly immunogenic. Several other prototype candidate vaccines are possible, including those based on the rubella virus component of the vaccine as a vector.