A number of investigators 1-4 have demonstrated the effectiveness of live, attenuated measles viruses in immunizing susceptible children against measles. However, the vaccinations caused a relatively high rate of generally mild reactions. A febrile response occurred in approximately 70%-80% of the children, reaching 105 F or above in some cases. A slight, measles-like rash was also observed in approximately 50%. McCrumb et al.,5 Reilly et al.,6 and Stokes et al.7 have recently demonstrated that these reactions could be reduced by the simultaneous use of γ-globulin.
Nevertheless, from a practical point of view, it appears highly desirable to develop a virus strain which will not produce any significant reactions when administered without γ-globulin and yet will cause the development of measles antibodies. We have therefore attempted to further modify the Edmonston strain of measles virus.1,2 This paper is a preliminary report on results obtained by testing our