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Flatten the Curve

Actualizado: 20 mar 2020

By Bernard Choi, PhD

Senior Research Scientist - Chercheur scientifique principal

Centre for Surveillance and Applied Research - Centre de surveillance et de recherche appliquée. Public Health Agency of Canada - Agence de la santé publique du Canada

785 Carling, Ottawa

AMNET funder member, since 2003

Background: Flatten the Curve has become the defining graphic of the COVID-19 pandemic. Community mitigation strategies, including social distancing, having people work from home, staying at home, school closure, are effective ways to slow the transmission of disease and to protect high risk individuals. This “flattens the curve”. Where does the term come from? What does it mean?

The Fact: The first instance of “Flatten the Curve” can be found in a 2007 CDC paper called “Interim pre-pandemic planning guidance: community strategy for pandemic influenza mitigation in the United States: early, targeted, layered use of nonpharmaceutical interventions”.(The paper has a long name with two colons so you won’t miss it). A graph (Fig. 1) compares the outcomes of a pandemic outbreak with and without intervention. Unfortunately the paper does not list any authors so we do not know whose bright idea it was. In 2017, when the paper was updated, the graphic lost its 1, 2, 3 numbering scheme.

The original idea has been repeatedly remixed by health experts to reach its current form. On 2020-02-28, the Economist published a modified version of the original 2007 graph to illustrate the spread of covid-19. On the same day on reading the Economist graph, Drew Harris, a professor, made an important contribution by adding an extra line to the graph. That made all of the difference. That extra line is the dotted “healthcare system capacity” line. The graph was hand-drawn and shared on Twitter that night. It was published in the New York Times on 2020-03-11.

On 2020-03-10, Tomas Pueyo in his paper “Coronavirus: Why You Must Act Now” produced an animated graph that has a wavy “medical research and treatment capacity” curve instead of a straight line. This perfects the concept.

What does it mean to “flatten the curve”? The ideal goal in fighting a 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. Think of the health care system capacity as a subway car that can only hold so many people at once. During rush hour, that capacity is not enough to handle the demand, so people must wait on the platform for their turn to ride. Staggering work hours diminishes the rush hour and increases the likelihood that you will get on the train and maybe even get a seat.

Source: The story behind ‘flatten the curve,’ the defining chart of the coronavirus. (2020-03-13);

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