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He helped coin the phrase “flatten the curve.” And he’s pretty impressed at how well some countries, and American states and cities, have done it in recent weeks.

By keeping as many people at home as possible, they’ve kept the numbers of serious cases of COVID-19 below or just above what hospitals in most areas can handle, says Howard Markel, M.D., Ph.D. of the University of Michigan Center for the History of Medicine.

And that, without a doubt, has saved lives. It’s also bought time for researchers to seek treatments and develop vaccines, and for public health agencies and hospitals to build up the testing and treatment capacity that must be in place before any “return to normal.”

But now, Markel worries that some of those places will squander the progress they’ve made.

SEE ALSO: Flattening the Curve for COVID-19: What Does It Mean and How Can You Help?

If they take recent signs of “flattening” as a signal to ease up on restrictions, they could end up with something just as bad as, or even worse than, an unflattened curve of COVID-19 cases.

Markel is worried about curves with a double peak.

Easing up on “social distancing” steps too soon, and too quickly, could give the novel coronavirus a chance to race back into broad circulation, he explains. Serious cases, and deaths, could spike again, and waste all the progress that has been made so far.

Lessons from the past

That’s exactly what happened in many cities during the flu pandemic of 1918 and 1919, as Markel and his colleagues showed in their detailed study of how non-pharmaceutical measures like school and business closings affected rates of excess deaths in dozens of U.S. cities.

SEE ALSO: Think This Flu Season Is Bad? Flash Back 100 Years

Even though the world of 2020 is far different from that of the World War I period, Markel sees the same thing happening today that happened then, and in other disease outbreaks he’s studied.

“In every pandemic, there’s a tug of war. On one end, there are the economic and business interests, and on the other end is the public’s health,” he says. “We know from history that when citizens become restless and protest to their leaders about lifting these sanctions too early, another rise in cases invariably occurs. In some places it was worse than the first peak.

“This creates a situation where you have endured shelter in place sanctions and crippled the economy for nothing,” says Markel, a professor of medicine, history and public health at U-M and member of the Institute for Healthcare Policy and Innovation.

Echoes in economic arguments

One hundred years ago, U-M Medical School dean Victor Vaughan described “bodies stacked like cord wood” during his trip to Boston to address the flu pandemic with the Army Medical Corps.

Images emerging in recent weeks from New York City and Detroit, of body bags in hospitals lining hallways and stacked in refrigerated trucks, evoke a modern version of what Vaughan saw.

But at the same time, Markel hears the calls, and even protests, for Michigan and other states to reopen now that the numbers of cases and deaths appear to be starting to level off, or even falling.

Those making an economic case for reopening businesses, schools and public places right now are also echoing the sentiments seen in the popular media of 1918 and 1919, Markel notes.