In addition, inactivating mutations in the type I interferon receptor IFNAR1 [45], the high-affinity interferon α/β receptor IFNAR2 [46], and the transcription factors signal transducer and activator of transcription (STAT) 1 [47] and STAT2 [48,49], which are involved in the control of cell responses to interferons, have been identified in children who developed disseminated infection or fatal encephalitis after inoculation of the live attenuated measles, mumps, and rubella vaccine. Here, IFNAR2 is linked to encephalitis.