As coronavirus lockdowns loosen and some Americans flock to restaurants, beaches, and other outdoor spaces for Memorial Day weekend, the question of reopening too quickly is striking an eerily familiar tone.

The global flu epidemic of 1918 remains the deadliest on record. According to the Centers for Disease Control and Prevention, the pandemic killed an estimated 50 million worldwide and over half a million in the United States. J. Alexander Navarro of the University of Michigan’s Center for History of Medicine is one of the organizers of the “Influenza Archive,” a collection of information cataloging and studying the effects of the 1918 pandemic in 43 major U.S. cities.

The research sought an answer to a key question: Was social distancing effective in 1918 as a way of slowing the spread of the disease and saving lives?

Navarro said cities that closed schools and banned public gatherings fared better against the flu. “They had both lower peak and total overall morbidity and mortality cases and deaths,” he said.

In fact, statewide orders making masks mandatory and shuttering nonessential businesses were widespread in 1918. San Francisco, for example, imposed fines on individuals failing to wear a mask in public, prompting protests.

Current research tracking the success of social distancing efforts to ease the spread of the novel coronavirus point to the same conclusion.