Fig. 1. Post-exposure vaccination window extrapolated from historical epidemiology reports. A review of references that described post-exposure vaccination as providingpartial or complete protection from, or attenuation of, smallpox symptoms during disease outbreaks was accomplished. The reported post-exposure vaccination windowswere charted (gray bars) by the days post-exposure that efficacious vaccination was administered (black horizontal axis text). The percentage of references that indicated abenefit to post-exposure vaccination prior to each day post-exposure (gray horizontal axis text) were determined.