Projections of epidemic transmission and estimation of vaccination impact during an ongoing Ebola virus disease outbreak in Northeastern Democratic Republic of Congo, as of Feb. 25, 2019

Worden, Lee; Wannier, Rae; Hoff, Nicole A.; Musene, Kamy; Selo, Bernice; Mossoko, Mathias; Okitolonda-Wemakoy, Emile; Muyembe Tamfum, Jean Jacques; Rutherford, George W.; Lietman, Thomas M.; Rimoin, Anne W.; Porco, Travis C.; Kelly, J. Daniel

A negative binomial autoregressive model was chosen through a validation process to forecast additional new case counts at time points one week, two weeks, four weeks, and eight weeks from the current date. To adjust for disparities in the frequency of case reporting in historic outbreaks, the data were weighted by the inverse square root of the number of observations contributed to the model. Models considered included parameters for historic cumulative case counts (probable and confirmed) at different time points, logs of historic case counts, ratio of historic case counts to try and capture the trend of the epidemic curve, log(time), and an offset for current case total. When historic case counts for specific dates were missing, each missing case count was linearly interpolated from the two nearest case counts, allowing the model to remain agnostic about the current trend of the epidemic. After model fitting and validation, the final model chosen was a log-link regression for additional cases on the number of new cases identified in the previous two and four weeks and the ratio of these two case counts.