This study is aimed at the evaluation of countermeasures in terms of the total number of patients and deaths, the number of vaccine doses used, and the time for eradication as examined through simulations of the outbreak of smallpox following a bioterrorist attack in the center of Okayama City. Three countermeasures were considered: traced vaccination (TV), mass vaccination (MV), and school closure.

An individual-based model was adopted, in which every individual is assigned their own personal information, behavioral pattern, and interactions among social settings to simulate the situation on a realistic basis. The influence of residual immunity obtained by past vaccination reflected age-dependent immunity to smallpox in Japan.

MV performed within a 2-day period at the same time in 10 school districts had the highest effectiveness in reducing the total number of patients and deaths among all simulations. Performing both TV and MV simultaneously was much more effective than performing TV or MV individually. The decrease in the number of patients with TV or MV in combination with school closure was faster than that by TV or MV without school closure.

According to the simulations results, it was advisable to carry out MV, or both TV and MV, simultaneously with school closure as countermeasures against a smallpox epidemic initiated by a bioterrorist attack.