Evaluating Subcriticality during the Ebola Epidemic in West Africa

The 2014–2015 Ebola outbreak is the largest and most widespread to date. In order to estimate ongoing transmission in the affected countries, we estimated the weekly average number of secondary cases caused by one individual infected with Ebola throughout the infectious period for each affected West African country using a stochastic hidden Markov model fitted to case data from the World Health Organization. If the average number of infections caused by one Ebola infection is less than 1.0, the epidemic is subcritical and cannot sustain itself. The epidemics in Liberia and Sierra Leone have approached subcriticality at some point during the epidemic; the epidemic in Guinea is ongoing with no evidence that it is subcritical. Response efforts to control the epidemic should continue in order to eliminate Ebola cases in West Africa.

[1]  S. Günther,et al.  Evidence for a Decrease in Transmission of Ebola Virus — Lofa County, Liberia, June 8–November 1, 2014 , 2014, MMWR. Morbidity and mortality weekly report.

[2]  John-Arne Røttingen,et al.  Efficacy and effectiveness of an rVSV-vectored vaccine expressing Ebola surface glycoprotein: interim results from the Guinea ring vaccination cluster-randomised trial , 2015, The Lancet.

[3]  G. Kitagawa.  A self-organizing state-space model , 1998 .

[4]  Adam Kucharski,et al.  Temporal Changes in Ebola Transmission in Sierra Leone and Implications for Control Requirements: a Real-time Modelling Study , 2015, PLoS currents.

[5]  Alicia Karspeck,et al.  Comparison of Filtering Methods for the Modeling and Retrospective Forecasting of Influenza Epidemics , 2014, PLoS Comput. Biol..

[6]  Carlos Castillo-Chavez,et al.  Temporal Variations in the Effective Reproduction Number of the 2014 West Africa Ebola Outbreak , 2014, PLoS currents.

[7]  Lauren Ancel Meyers,et al.  Epidemiological and viral genomic sequence analysis of the 2014 ebola outbreak reveals clustered transmission. , 2015, Clinical infectious diseases : an official publication of the Infectious Diseases Society of America.

[8]  Martin Enserink.  The Ebola Epidemic. High hopes for Guinean vaccine trial. , 2015, Science.

[9]  T. Lancet.  Ebola: a failure of international collective action , 2014, The Lancet.

[10]  Wayne T. A. Enanoria,et al.  Identifying postelimination trends for the introduction and transmissibility of measles in the United States. , 2014, American journal of epidemiology.

[11]  Mikiko Senga,et al.  Ebola virus disease in West Africa--the first 9 months of the epidemic and forward projections. , 2014, The New England journal of medicine.

[12]  L. Boulanger,et al.  Ebola Epidemic — Liberia, March–October 2014 , 2014, MMWR. Morbidity and mortality weekly report.

[13]  Sasikiran Kandula,et al.  Inference and Forecast of the Current West African Ebola Outbreak in Guinea, Sierra Leone and Liberia , 2014, PLoS currents.

[14]  J. Medlock,et al.  Strategies for containing Ebola in West Africa , 2014, Science.

[15]  Alison P Galvani,et al.  Effect of Ebola progression on transmission and control in Liberia. , 2015, Annals of internal medicine.

[16]  Jonathan Dushoff,et al.  Modeling Post-death Transmission of Ebola: Challenges for Inference and Opportunities for Control , 2014, Scientific Reports.

[17]  N. Gordon,et al.  Novel approach to nonlinear/non-Gaussian Bayesian state estimation , 1993 .

[18]  Gerardo Chowell,et al.  The Western Africa Ebola Virus Disease Epidemic Exhibits Both Global Exponential and Local Polynomial Growth Rates , 2014, PLoS currents.

[19]  Norman T. J. Bailey.  The Elements of Stochastic Processes with Applications to the Natural Sciences , 1964 .

[20]  Gerardo Chowell,et al.  Is West Africa Approaching a Catastrophic Phase or is the 2014 Ebola Epidemic Slowing Down? Different Models Yield Different Answers for Liberia , 2014, PLoS currents.

[21]  C. Althaus.  Estimating the Reproduction Number of Ebola Virus (EBOV) During the 2014 Outbreak in West Africa , 2014, PLoS currents.

[22]  Alessandro Vespignani,et al.  Assessing the International Spreading Risk Associated with the 2014 West African Ebola Outbreak , 2014, PLoS currents.

[23]  W. Gilks,et al.  Following a moving target—Monte Carlo inference for dynamic Bayesian models , 2001 .

[24]  W. Team.  Ebola Virus Disease in West Africa — The First 9 Months of the Epidemic and Forward Projections , 2014 .

[25]  D. Fisman,et al.  Early Epidemic Dynamics of the West African 2014 Ebola Outbreak: Estimates Derived with a Simple Two-Parameter Model , 2014, PLoS currents.

[26]  G. Chowell,et al.  Transmission dynamics and control of Ebola virus disease (EVD): a review , 2014, BMC Medicine.

[27]  Mit Philips,et al.  Ebola: a failure of international collective action , 2014, The Lancet.

[28]  D. E. Barton,et al.  The Elements of Stochastic Processes with Applications to the Natural Sciences , 1964 .

[29]  G. Kitagawa.  Theory and Methods , 1998 .

[30]  T. Nyenswah,et al.  Evidence for Declining Numbers of Ebola Cases — Montserrado County, Liberia, June–October 2014 , 2014, MMWR. Morbidity and mortality weekly report.

[31]  Alessandro Vespignani,et al.  Spatiotemporal spread of the 2014 outbreak of Ebola virus disease in Liberia and the effectiveness of non-pharmaceutical interventions: a computational modelling analysis. , 2015, Lancet. Infectious Diseases (Print).

[32]  J. Wallinga,et al.  Different Epidemic Curves for Severe Acute Respiratory Syndrome Reveal Similar Impacts of Control Measures , 2004, American journal of epidemiology.

[33]  Suzanne M. O’Regan,et al.  Ebola Cases and Health System Demand in Liberia , 2014, PLoS biology.

[34]  C. Dolea,et al.  World Health Organization , 1949, International Organization.