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

There are limitations to our projections. Projection distributions are right-skewed, with long tails (and we therefore report the median instead of the mean). We were unable to include all the 23 observed EVD outbreaks with a case count greater than ten cases in our estimates due to data availability. Our regression models are based entirely on past outbreaks of Ebola virus disease (measured and reported in different ways), and cannot account for the improved Projections of an EVD outbreak in Northeastern DRC control measures and vaccination in the way that a mechanistic model does. We included as much real-time information in our models as possible, but situations such as the introduction of EVD into a zone of armed conflict and the recent introduction of vaccination are not reflected by the suite of past outbreaks. The stochastic model used estimated vaccination effectiveness, reported cases, and timing of onset dates affected by vaccination from studies from West Africa, not DRC, and did not include vaccination of healthcare workers. Our forecasts do not account for possible unreported cases or changes in reporting over time; such gaps in reporting can not be ruled out, though given the intense efforts at case finding that started in July and carried forward, we think it unlikely that there were large changes in reporting. Furthermore, as the outbreak moved into areas affected by violent conflict as the outbreak continued, we think it likely that case reporting, if anything, decreased over time, and therefore underreporting would not explain the apparent increase in transmission from June to October. While it would be desirable to use the vaccination coverage estimates to estimate the number of cases prevented by the vaccination program, our models were not designed to produce a testable estimate of such an effect.