Flattening the Coronavirus Curve

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One chart explains why slowing the spread of the infection is nearly as important as stopping it.

At the end of February, Drew Harris, a population health analyst at Thomas Jefferson University in Philadelphia, had just flown across the country to visit his daughter in Eugene, Ore., when he saw an article on his Google news feed. It was from The Economist, and was about limiting the damage of the coronavirus.

The accompanying art, by the visual-data journalist Rosamund Pearce, based on a graphic that had appeared in a C.D.C. paper titled “Community Mitigation Guidelines to Prevent Pandemic Influenza,” showed what Dr. Harris called two epi curves. One had a steep peak indicating a surge of coronavirus outbreak in the near term; the other had a flatter slope, indicating a more gradual rate of infection over a longer period of time.

The gentler curve ultimately results in fewer people infected and fewer deaths. “What we need to do is flatten that down,” said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, during the coronavirus task force briefing at the White House on Tuesday evening. “You do that with trying to interfere with the natural flow of the outbreak.”

The infographic reminded Dr. Harris of something similar that he had designed years earlier for a pandemic preparedness training program. “Folks in the preparedness and public health community have been thinking about all of these issues for many years,” Dr. Harris said in an email. “Understanding and managing surge is an important part of preparedness.” But during the training course, Dr. Harris’s students had struggled with the concept of reducing the epidemic curve, so he added a dotted line indicating hospital capacity — “to make clear what was at stake,” he said.

After his visit with his daughter, Dr. Harris was waiting for his return flight in Portland when the first Oregon coronavirus case was announced; he had dinner at a busy airport bar and thought about how quiet the place would be in a week or two when the reality of the outbreak set in. Once home, he recreated his graphic and posted it on Twitter and LinkedIn, and was pleased to see the enthusiastic interest in flattening the curve.

The following is an edited version of our email conversation.

What does it mean to “flatten the curve”?

“Now I know what going viral means,” Dr. Harris said. (For a more detailed analysis, see a recent paper in The Lancet, “How will country-based mitigation measures influence the course of the COVID-19 epidemic?”)

The ideal goal in fighting an epidemic or pandemic is to completely halt the spread. But merely slowing it — mitigation — is critical. This reduces the number of cases that are active at any given time, which in turn gives doctors, hospitals, police, schools and vaccine-manufacturers time to prepare and respond, without becoming overwhelmed. Most hospitals can function with 10 percent reduction in staff, but not with half their people out at once.

Some commentators have argued for getting the outbreak over with quickly. That is a recipe for panic, unnecessary suffering and death. Slowing and spreading out the tidal wave of cases will save lives. Flattening the curve keeps society going.