VACCINATION against smallpox carries with it a known risk of postvaccination encephalitis. The rate of incidence of this complication is not constant. The numerous reports of encephalitis following smallpox vaccination show that the incidence varies not only in different localities but also in the same locality in different years. In Tyrol, for instance, a rate of 1 case of encephalitis to 641 vaccinations was reported in 1929, while an incidence ratio of 1: 4570 was observed in 1927.1 In the United States, 1 case in 350 vaccinations occurred in the years 1928 to 1930, but a ratio of 1: 1000 was recorded in a large city in 1930.2
A presumptive diagnosis of postvaccination encephalitis is usually made on the basis of the onset, 7 to 14 days after vaccination, of an acute illness, with fever, headache, vomiting, change in the mental state, signs of meningeal irritation, paralyses, and
DOLGOPOL VB, GREENBERG M, ARONOFF R. ENCEPHALITIS FOLLOWING SMALLPOX VACCINATION. AMA Arch NeurPsych. 1955;73(2):216–223. doi:10.1001/archneurpsyc.1955.02330080094018
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