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Post-Vaccinial Encephalitis: Frequency & Susceptible Populations
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Post-Vaccinial Encephalitis (PVE) Cases per 1,000,000 Primary Vaccinations(*)

Age (yrs)

 1968 National
Survey(†)

1968 10-State
Survey(§)

1-4 2.0 9.5
5-19 2.3 8.7
>20 3.5 0
Totals > 1 yr 2.4 8.6

* Numbers rounded to the nearest tenth, total number of vaccinations estimated in both studies. Observations missing age were distributed according to the existing age distribution for PVE.
† Case sources include: American Red Cross Vaccinia Immune Globulin (VIG) distribution system, Red Cross VIG consultants, State and Territorial Epidemiologists, Burroughs-Wellcome Thiosemicarbazone distribution list, smallpox vaccine manufacturers complication reporting files, state reports to the Encephalitis Surveillance Unit of the National Communicable Disease Center (NCDC), and specimen submissions for vaccinia testing to the Viral Exanthems Unit of NCDC.
§ Case sources include: Physician reporting via survey in 10 states with active case information follow-up and chart review for PVE and vaccinia necrosum reports.

European data indicate a higher incidence than in the U.S., but whether this reflects the use of different vaccine strains or differences in diagnostic methods is unknown. There are no known predictive antecedents.