title: Modeling the 2014 Ebola Virus Epidemic - Agent-Based Simulations, Temporal Analysis and Future Predictions for Liberia and Sierra Leone.
abstract: We developed an agent-based model to investigate the epidemic dynamics of Ebola virus disease (EVD) in Liberia and Sierra Leone from May 27 to December 21, 2014. The dynamics of the agent-based simulator evolve on small-world transmission networks of sizes equal to the population of each country, with adjustable densities to account for the effects of public health intervention policies and individual behavioral responses to the evolving epidemic. Based on time series of the official case counts from the World Health Organization (WHO), we provide estimates for key epidemiological variables by employing the so-called Equation-Free approach. The underlying transmission networks were characterized by rather random structures in the two countries with densities decreasing by ~19% from the early (May 27-early August) to the last period (mid October-December 21). Our estimates for the values of key epidemiological variables, such as the mean time to death, recovery and the case fatality rate, are very close to the ones reported by the WHO Ebola response team during the early period of the epidemic (until September 14) that were calculated based on clinical data. Specifically, regarding the effective reproductive number Re, our analysis suggests that until mid October, Re was above 2.3 in both countries; from mid October to December 21, Re dropped well below unity in Liberia, indicating a saturation of the epidemic, while in Sierra Leone it was around 1.9, indicating an ongoing epidemic. Accordingly, a ten-week projection from December 21 estimated that the epidemic will fade out in Liberia in early March; in contrast, our results flashed a note of caution for Sierra Leone since the cumulative number of cases could reach as high as 18,000, and the number of deaths might exceed 5,000, by early March 2015. However, by processing the reported data of the very last period (December 21, 2014-January 18, 2015), we obtained more optimistic estimates indicative of a remission of the epidemic in Sierra Leone, as reflected by the derived Re (~0.82, 95% CI: 0.81-0.83).
authors.affiliation: Applied Mathematics and Physical Sciences, National Technical University of Athens, Athens, Greece.
authors.forename: Constantinos
authors.initials: C
authors.lastname: Siettos
authors.affiliation: Division of Genetics, Cell and Developmental Biology, University of Patras, Patras, Greece.
authors.forename: Cleo
authors.initials: C
authors.lastname: Anastassopoulou
authors.affiliation: Consiglio Nazionale di Ricerca, Napoli, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Russo
authors.affiliation: Division of Infectious Diseases, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA.
authors.forename: Christos
authors.initials: C
authors.lastname: Grigoras
authors.affiliation: Division of Infectious Diseases, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA.
authors.forename: Eleftherios
authors.initials: E
authors.lastname: Mylonakis
keywords: Agent-Based Simulations; Contact Network; EBOV; Effective reproductive number (Re); Equation-free approach; Forecasting; ebola