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Containing a Smallpox Attack: Population Structure, Disease Spread, and Control Policy Effectiveness
Summary: Dr. Ferguson conducts research on the development of robust methodologies for the quantitative analysis and prediction of patterns of infectious disease spread and evolution, as they apply to the design of control and treatment programs.
Predicting the initial spatial spread of an infectious disease outbreak is critical in developing contingency plans for a bioterrorist attack or novel disease outbreaks. Factors such as the size, density, and structure of human populations have a substantial impact on patterns of epidemic spread. Detailed data on some of these factors are available for many countries. We explore the effect of population structure of disease spread and control policy effectiveness using a simulation model of epidemic spread in the UK population. We assume that a susceptible individual can become infected through three possible routes: in the household, via a network of contacts built up at work, or from a chance face-to-face meeting with a stranger. UK Census data (with approximately 1-2km spatial resolution) are used to estimate household sizes, densities and location-specific movement distributions. The movement distributions we use describe commuting behavior, giving the probability that an individual resident at one spatial location travels to work at any other location in the UK. We find that initial epidemic spread is sensitive to the balance between routes of infection, with the rate of spatial spread being lower if infections primarily occur within households. We have applied the model to examine the relative efficiency of different options for the containment of a smallpox deliberate release scenario. Our results illustrate how the effectiveness and likely ease of implementation of vaccination programs relying upon tracing of contact of diagnosed cases depends critically on the relative importance of the three transmission routes considered. We have modeled the efficiency and effectiveness of regional or countrywide mass-vaccination strategies, taking possible logistical constraints into consideration. We argue that current uncertainties about likely smallpox epidemiology in modern contexts highlight the need for tiered responses with clear criteria for vaccination switching based on a realtime assessment of policy effectiveness.
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