In this 1918 photo made available by the Library of Congress, volunteer nurses from the American Red Cross tend to influenza patients in the Oakland Municipal Auditorium, used as a temporary hospital. Credit: Edward A. Rogers | Library of Congress

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Maine Gov. Janet Mills is working to formulate a plan to safely ease restrictions on business, travel and other activities put in place to slow the spread of the new coronavirus. President Donald Trump, last week, unveiled guidelines for allowing such restrictions to be lifted where conditions — such as a sustained 14-day drop in new cases — are met.

Still, small but vocal groups of protesters have gathered in state capitals around the country, including in Augusta, to call for a more rapid return to normalcy.

As governors and others consider next steps, lessons from the 1918 flu pandemic can be instructive.

[Our COVID-19 tracker contains the most recent information on Maine cases by county]

First, although the deadly illness is often referred to as the Spanish flu, it likely did not originate in Spain. Although the exact source of the virus has not been found, historians believe that someone from Kansas carried the flu to an Army base there, where it quickly spread in the spring of 1918. American soldiers then carried it to Europe as they were shipped there during World War I. American soldiers brought a more virulent version of the flu back to America, with large outbreaks in port cities where large numbers of troops were welcomed home.

One of the most important things to know about the 1918 flu is that it was not a one-time event. There were three waves of the illness, and the second and third waves were more deadly than the first.

The first wave, in the spring of 1918, was not particularly lethal with many people recovering within three days. But, in the fall of 1918, the flu had become much more virulent and the mortality rate associated with the illness during this second wave was staggering. In October alone, 195,000 Americans died from the flu.

A third wave began in Australia in early 1919 and the flu again made its way around the world. This wave was not as deadly as the second, but caused more deaths than the first.

All told, more than 50 million people died from the outbreak and a third of the world’s population was infected.

Another crucial lesson to keep in mind is that physical distancing and stay-at-home orders work, and should be lifted carefully based on data, not political pressure.

Researchers who have studied the 1918 flu conclude that states and cities that followed public health recommendations about how the disease spread generally had fewer deaths than those that did not. San Francisco, for example, was the first city to order a lockdown and its health director urged residents to wear masks. The city was spared from high death rates in the first and second rounds, but not the third.

Officials in Philadelphia, along with federal officials, downplayed the severity of the illness. Rather than implement social distancing protocols, as many cities did, Philadelphia held a large victory parade in late September 1918. Within weeks, 4,500 people had died in the city.

“In every city we studied from this era there was public pressure to quit the social distancing measures as soon as the epidemic seemed to peak and then ebb,” J. Alexander Navarro and Howard Markel wrote in a recent Washington Post piece. The two are co-editors-in-chief of “The American Influenza Epidemic of 1918: A Digital Encyclopedia ” and direct the Center for the History of Medicine at the University of Michigan.

“Thinking that the proverbial coast was clear, many communities lifted social distancing measures before the battle was truly over,” they wrote. “After weeks of being denied their usual social outlets, people were eager to return to a life of normalcy, and they did so in one giant rush. In city after city, masses lined up for movie houses and performance theaters, crowds packed into dance halls and cabarets, and throngs flocked to downtown shopping districts, often on the very day that the closure orders were lifted.

“The result? Cases and deaths resurged,” Navarro and Markel warned.

This isn’t just century-old history. The head of the U.S. Centers for Disease Control and Prevention warned Tuesday that a second wave of coronavirus could be more devastating than the current one.

“There’s a possibility that the assault of the virus on our nation next winter will actually be even more difficult than the one we just went through,” CDC Director Robert Redfield said in an interview with The Washington Post.

He warned that the coronavirus and seasonal flu could be happening at the same time, putting a huge strain on our health care system. Even if stay-at-home orders are lifted, Redfield urged a continuation of social distancing. He also urged a significant increase in testing and contact tracing capabilities to track the illness.

The biggest lesson is that science — not political expediency or public opinion — should drive any decisions about easing requirements on individuals and businesses.