THE DIAGNOSIS of postvaccination encephalitis has posed a problem to the clinician ever since it was established as a definite clinical entity.
The program for large scale vaccination which took place in New York city during 1947 well illustrated the difficulties of attaining the correct diagnosis. More than 6,350,000 persons were vaccinated in a period of one month. Within two and one-half months after the vaccination program was instituted, 50 cases of possible encephalitis were reported to the department of health. Four of these cases were ruled out as definitely not encephalitis. In the remaining 46 cases, the diagnosis was considered probable. Death resulted in 8 of these cases. Brain tissue in each of the fatal cases was examined, and in none of them were the characteristic lesions of postvaccination encephalitis observed. Autopsy showed that 2 of the deaths were caused by tuberculous meningitis, 1 by brain tumor, 1 by