The “Flatten the Curve” Chart Was Ugly and Not Scientifically Rigorous. Why Did It Work So Well?

The first version of the now-ubiquitous “flatten the curve” chart appeared in a 2007 report by the Centers for Disease Control and Prevention. The image, titled “Goals of Community Mitigation,” accompanied a list of radical recommendations to swiftly change American life in the event of a pandemic: close schools, cancel public gatherings, recommend voluntary isolation. The authors used a now-familiar term for the strategy: “social distancing.”

The colors have changed, but the chart then was more or less what we see today. Two ugly humps: one purple and steep, representing...