From 1963 through 1971, eighty-four cases of neurologic disorders with onset less than 30 days after live measles-virus vaccination were reported in the United States. Thirteen could be adequately accounted for by causes other than vaccine, and another 11 were uncomplicated febrile convulsions probably related to vaccination. One case met diagnostic criteria for subacute sclerosing panencephalitis. The remaining 59 showed clinical features of encephalitis or encephalopathy. Causes of these cases could not be established, but 45 (76%) had onset between 6 and 15 days after vaccination; this clustering suggests that some may have been caused by vaccine. From 1963 through 1971, 50.9 million doses of measles vaccine were distributed, and, therefore, incidence of the reported neurologic disorders was 1.16 per million doses. Risk of encephalitis following measles infection is one per thousand cases.
Philip J. Landrigan, John J. Witte. Neurologic Disorders Following Live Measles-Virus Vaccination. JAMA. 1973;223(13):1459–1462. doi:10.1001/jama.1973.03220130011003