The Economist, 25 July 2020

Modest Changes in Behavior leads to “huge rises in coronavirus infections”: The Geometry of the Pandemic, p. 19

This article focuses on a model by Rajiv Rimal of Johns Hopkins University. And it’s a big, fat chunk of the article (maybe a third), longer than she usually manages to quote. But she wanted to share it. Knowledge is power!

When “American states began easing lockdowns . . . their caseloads were three or more times higher than in Europe, in part, argues Jarbas Barbosa of the Pan-American Health Organization, because most states never had full lockdowns. Texas had 1,270 new cases on the day its governor said restaurants could reopen: 44 per million. In Georgia, the rate was 95 per million. Disney World reopened the day before Florida announced a record 15,000 new cases in a day. Just as incredibly, in two-thirds of states, infections were rising when governors started to ease lockdowns. By contrast, France, Spain and Italy had 13-17 new cases per million when they began to re-open their economies and numbers were falling fast.

“On April 12th … 95% of the population was staying at home (leaving the house only for essential visits), with 5% ignoring lockdown rules. Based on those assumptions, his model predicts that Americans would have had 559,400 cases on that day — an accurate assessment (it actually had 554,849). On July 14th, Mr. Rimal assumed that 80% of the population was staying at home, i.e., only a gradual change. On this basis, his model predicts the country would have 1.6m cases, again not far off the actual number and confirming the impact of modest rises in activity. If people really altered their behaviour, the number would rise even further to 5.6m cases if the stay-at-home share drops to 60% and to 9.5m if it falls to 20%. In that worst case, America’s death toll could top 400,000. Such is the dark logic of geometric growth.”

The Economist concludes that “to drive the level of infection down to perhaps a tenth of what it is now (closer to European or Asian levels) … seems to require full lockdowns.”

Stay safe, dear blog readers. Stay safe.

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