The graph above was pulled from this article.
The pandemic Spanish flu of 1918 was the Influenza A subtype H1N1 virus. According to the CDC, it was first identified in the spring, and about 500 million people or 1/3 of the world’s population became infected. The death toll was estimated at 50 million worldwide and 675,000 in the U.S.
At that time, there were no antibiotics to fight the secondary complications caused by the flu, and our medical technology was far inferior to what it is today. The main way to control the spread of disease was through isolation.
There is a famous case history from this time looking at Philadelphia and St. Louis
Philadelphia did not implement social distancing and experienced a significant surge in cases while St. Louis closed the city down and very effectively decreased the spread. Just for comparison, some statistics on the seasonal flu virus, according to the CDC.
2018: 42.9 million people got sick, 647,000 hospitalized and 61,200 died
2019: 3.7 million people go sick, about 41,000 hospitalizations and approximately 3,300 flu-related deaths
Social Distancing Is Necessary to Help Flatten the Curve