In 1918, when the so-called Spanish Flu was raging (it was only first reported by Spanish journalists, although it likely began elsewhere), an incredibly powerful lesson was learned through a natural experiment that involved two major American cities. Remember that this deadly virus killed at least 50 million people world-wide and nearly 700,000 Americans. Although these were days long before modern medicine and vaccines, ICUs, and mechanical ventilators, it’s worth revisiting some of those lessons.

In Philadelphia, the city’s response mirrored much of the Trump Administration’s early leisurely tone: authorities downplayed the significance of the threat after the first case was reported on September 17, 1918, and large events weren’t canceled. Notably, the city’s liberty parade – which drew 200,000 Philadelphians to crowded city streets – took place eleven days later on Sept. 28th. By the time social distancing measures and school and restaurant closures were implemented (by October 3rd), it was too late. The virus had spread, overwhelming the city’s public health capacity, law enforcement, and causing the death total to surge to over 17,500 in just six months.

But just several hundred miles away in St. Louis, an entirely different story was playing out. With the first cases of influenza reported on October 5th, the city was shut down by October 7th. Schools, playgrounds, and churches were shuttered, while public gatherings of over 20 people were prohibited. The intervention worked: per capita influenza deaths in St. Louis (347 deaths/100,000 people) were less than half than those of Philadelphia (719/100,000).  

Juxtaposing the response of the two cities highlights how quick public health responses can save countless lives. Visualizing the cases of Philadelphia and St. Louis also highlights exactly the notion of ‘flattening the curve.’ While neither city was able to prevent the spread of influenza, St. Louis prevented a spike in the death rate of the virus by mitigation efforts that prevented overwhelming the city’s healthcare system.

Of course, the Spanish flu of 1918 was entirely different from today’s novel coronavirus. But much of the policy prescriptions remain true: social distancing and quarantines can, and do, have a significant effect, if implemented and adopted rapidly, and maintained for the duration of the outbreak.

Source: Richard J. Hatchett, Carter E. Mecher, and Marc Lipsitch, “Public health interventions and epidemic intensity during the 1918 influenza pandemic.” Princeton University, 2007. https://www.pnas.org/content/104/18/7582