The current Covid-19 pandemic has drawn many references to the great flu pandemic of 1918. One of the natural experiments that emerged from that event is how different measures adopted by different cities led to significantly different outcomes, with those taking action more quickly effectively flattening the curve and having better outcomes than those that delayed doing so. While multiple non-pharmaceutical interventions such as reducing contacts among people were effective in reducing transmission of the virus, relaxation of those restrictions also resulted in renewing the spread of the virus.

This paper published in the PNAS in 2007 discusses that pandemic.

Nonpharmaceutical interventions (NPIs) intended to reduce infectious contacts between persons form an integral part of plans to mitigate the impact of the next influenza pandemic. Although the potential benefits of NPIs are supported by mathematical models, the historical evidence for the impact of such interventions in past pandemics has not been systematically examined. We obtained data on the timing of 19 classes of NPI in 17 U.S. cities during the 1918 pandemic and tested the hypothesis that early implementation of multiple interventions was associated with reduced disease transmission. Consistent with this hypothesis, cities in which multiple interventions were implemented at an early phase of the epidemic had peak death rates ≈50% lower than those that did not and had less-steep epidemic curves. Cities in which multiple interventions were implemented at an early phase of the epidemic also showed a trend toward lower cumulative excess mortality, but the difference was smaller (≈20%) and less statistically significant than that for peak death rates. This finding was not unexpected, given that few cities maintained NPIs longer than 6 weeks in 1918. Early implementation of certain interventions, including closure of schools, churches, and theaters, was associated with lower peak death rates, but no single intervention showed an association with improved aggregate outcomes for the 1918 phase of the pandemic. These findings support the hypothesis that rapid implementation of multiple NPIs can significantly reduce influenza transmission, but that viral spread will be renewed upon relaxation of such measures. [My emphasis-MS]

This graph of the cities of Philadelphia and St. Louis illustrate the difference between the outcomes.

In this clip, David Remnick, editor of The New Yorker, talks with historian John M. Barry, author of a book on the 1918 flu pandemic, about the comparisons with the current pandemic and what we can learn from it.

This article describes what daily life was like during the 1918 pandemic.