Comparison of the Two Edge Scenarios

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Sensitivity Analysis of the Model

Many parameters of the "Smallpox Attack" model are estimates that could vary widely in a real-life situation. For example, the authors estimate that the number of vaccinators in a city of ten million is 5000, and the number of people identified as contacts of an index case is, on average, 50. In reality, many of these parameters could deviate from the values in the model.

Two of the most critical parameters are the fraction of the population initially infected and the disease reproductive ratio. The first reflects the severity of a bioterrorist attack, while the second is equal to the number of people infected by an infectious individual in a day. These parameters are also two of the most uncertain ones. They are subject to differences in terrorist strategy and in disease strain.

In the base-case modeled in the previous slides, the number of people initially infected was 1000, which is equal to 0.1E-3 of the total population, and the basic reproductive ratio was set to 3. Here, we vary both of these parameters simultaneously and measure the effect on the total number of casualties.

Figure 3: Sensitivity Analysis for MV/TV Scenarios

In the graphs above, we explore what would happen if the basic reproductive ratio and the initial scale of the attack are increased well beyond their base-case values. In particular, basic reproductive ratio varies between 1 and 20, while the initial ratio of infected people to the rest of the population varies from 1e-3 to 10e-3. Note that as we approach the high end of these values, casualties under Mass Vaccination increase a lot slower than those under Trace Vaccination.

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