RISK ASSESSMENT AND RISK COMMUNICATION STRATEGIES IN BIOTERRORISM PREPAREDNESS 1 Preparing for a smallpox bioterrorist attack: pulse vaccination as an optimal strategy Zvia Agur 1 , Karen Marron 1 , Hanita Shai 1 , Yehuda L. Danon 2 1. Institute for Medical BioMathematics (IMBM); 10 Hate’ena St.; P.O.B. 282, 60991; Bene Ataroth, Israel 2. Kipper Institute of Immunology; Schneider Children Medical Center; FMRC; Petach-Tikva, 49202; Israel Events of recent years have significantly increased our awareness of the potential threat of a bioterrorist attack, and the smallpox variola virus has been identified as an “eligible candidate” for a biological warfare agent. Epidemiological mathematical modeling has long been recognized as a crucial tool for assessing the repercussions of such a viral outbreak, as well as for comparing possible response strategies. Several studies have applied mathematical models with the hope of identifying an optimal vaccination strategy in case of an attack [1–4]. However, these particular studies do not produce clear-cut recommendations, upon which authorities can rely when formulating policies. In fact, conclusions of certain studies contradict those of others. This inconsistency may stem from simulation results’ extreme sensitivity to the value assumed for the disease’s basic reproduction rate (R 0 ) [5], i.e. the number of secondary infections that an infectious individual is expected to produce if introduced into an entirely susceptible population. Because smallpox was eradicated in 1979, there is a lack of current epidemiological data on the disease, and R 0 must be estimated. However, as this value is dependent both on biological factors and on population