The CDC’s Ebola Predictions in September Were Reasonable

There is some talk online and in the conservative media that the predictions made by the Centers for Disease Control and Prevention back in September regarding potential Ebola cases by January 2015 were hysterical exaggerations.

Actually, they were not. For all its failings surrounding the Ebola response — I’d argue the response was too timid, and an under-reaction instead of an over-reaction — the CDC’s September projections were entirely reasonable.

Needless to say, back in September all major international media outlets were covering this CDC estimate.

The original CDC prediction from September reads as follows:

“By September 30, 2014, CDC estimates that there will be approximately 8,000 cases, or as high as 21,000 cases if corrections for underreporting are made. Without additional interventions or changes in community behavior, CDC estimates that by January 20, 2015, there will be a total of approximately 550,000 Ebola cases in Liberia and Sierra Leone or 1.4 million if corrections for underreporting are made.”

This projection came from a CDC report also released in September entitled “Estimating the Future Number of Cases in the Ebola Epidemic — Liberia and Sierra Leone, 2014-2015.” The authors used Ebola case data up to August 31, 2014.

Anyone can download the cumulative reported Ebola case data for Liberia and Sierra Leone from the CDC. Between July 28 and August 28, the number of Ebola cases in these two countries increased by a factor of 3.1 from 774 to 2,404. The rate of increase between the end of June and end of July was also about the same. Thus, when this CDC report was written in early September using data from up to the end of August, Ebola cases in Liberia and Sierra Leone were consistently increasing by a factor of about 3.1 per month.