Pandemic Reemergence and Four Waves of Excess Mortality Coinciding With the 1918 Influenza Pandemic in Michigan: Insights for COVID-19

Abstract

The global influenza pandemic that emerged in 1918 has become the event of reference for a broad spectrum of policymakers seeking to learn from the past. This article sheds light on multiple waves of excess mortality that occurred in the US state of Michigan at the time with insights into how epidemics might evolve and propagate across space and time. We analyzed original monthly data on all-cause deaths by county for the 83 counties of Michigan and interpreted the results in the context of what is known about the pandemic. Counties in Michigan experienced up to four waves of excess mortality over a span of two years, including a severe one in early 1920. Some counties experienced two waves in late 1918 while others had only one. The 1920 wave propagated across the state in a different manner than the fall and winter 1918 waves. The twin waves in late 1918 were likely related to the timing of the statewide imposition of a three-week social distancing order. Michigan's experience holds sobering lessons for those who wish to understand how immunologically naïve populations encounter novel viral pathogens.

FIGURE 1—

The Four Waves of Excess Deaths in Michigan: 1918–1920

FIGURE 2—

A Screenshot From the Centers for Disease Control and Prevention’s Web Site Commemorating the Pandemic and Showing the Spring (Herald), Fall, and Winter 1918 “Waves”

FIGURE 3—

Excess Deaths During (a) the Second (Fall 1918) and Third (Winter 1918) Waves and (b) the Fourth (Spring 1920) Wave: Highly Populated Counties in Michigan

FIGURE 4—

Peak Influenza Pandemic Weeks in Michigan Counties on the Weeks of (a) October 13, 1918, (b) December 15, 1918, and (c) February 15, 1920 Notes. Part a shows counties in which the Fall 1918 wave was higher than the Winter 1918 wave with their status the week of October 13, 1918. Part b shows counties in which the Winter 1918 wave was higher than the Fall 1918 wave with their status the week of December 15, 1918. Part c shows the status of the 1920 wave in Michigan counties the week of February 15, 1920. Note the simultaneous statewide peak in 1920 in contrast to the spatially distributed peaks in 1918 (a and b).