COVID-19: The Power of Historical Lessons

Eighty-nine million cases and 1.9 million deaths from coronavirus disease 2019 (COVID-19) have been reported up to January 8, 2021 (but these estimates are unfortunately going to increase),¹ and several countries now seem to be entering a third wave of the pandemic after the holiday season. Although several countries have started to vaccinate against COVID-19, pressing questions persist, including whether we will have more peaks or waves of the pandemic, how severe they will be, and how and when the pandemic will end.

THE 1918 PANDEMIC AS A BENCHMARK FOR COVID-19

Projections about the future can only be as good as the assumptions put into models, and errors tend to increase the farther out one tries to project. Although history will likely not repeat itself exactly, clues to the questions raised earlier nevertheless might be found in research on previous pandemics. The 1918 influenza pandemic is often used as a benchmark of comparisons with other past pandemics; the current COVID-19 pandemic; and future pandemics that might be caused by influenza, coronavirus, or an unknown pathogen and could be even deadlier. The 1918 pandemic is different from the COVID-19 pandemic in many ways—for example, it happened in the context of World War I more than 100 years ago, was caused by influenza and not coronavirus, and killed young adults rather than the elderly. However, these pandemics also have several similarities, including the populations at risk medically (e.g., people with lung and heart diseases) and those who are vulnerable socially (e.g., poor, immigrant, and Indigenous people).^2,3 The role of nonpharmaceutical interventions, such as handwashing, social distancing, and travel restrictions, in infection mitigation is another lesson from historic pandemics that appears translatable to COVID-19.^4,5

The earliest studies on the waves of the 1918 influenza pandemic have considered, for example, the number, severity, height, and length of waves, as well as possible cross-protection between them. This research has focused mainly on the second, most lethal fall wave and recently to some extent on the possible herald spring wave in 1918⁶; few studies have focused on the fourth and last wave in 1920. In this issue of AJPH, Chandra et al. (p. 430) present research in which they used monthly data on all-cause deaths for the 83 counties of Michigan to study the wavelike behavior of the 1918 to 1920 influenza pandemic. They found that Michigan had “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, whereas others had only one.” They also document that the two waves in late 1918 were likely related to the timing of the statewide imposition of a three-week social distancing order. Once this measure was lifted, infections and deaths started to increase again. Other research has shown similar effects in 1918,⁵ and we also have seen this outcome during the COVID-19 pandemic.

This research on the epidemiology of the 1920 wave and the demonstration of the value of public health in controlling the 1918 influenza pandemic are novel and historically important. Future studies could analyze the wavelike behavior of the 1918 influenza pandemic among subgroups with particular medical (e.g., age, comorbidities) and social (e.g., gender, socioeconomic status, race/ethnicity) variables. However, these results are even more important when they are used to speculate about the future course of COVID-19. The early spread of the COVID-19 pandemic was not consistent across the United States or elsewhere. Some areas experienced only peaks and troughs in a single wave, others have already seen several waves, and more peaks and troughs or even new waves have started or will occur. Future spread likely will not manifest equally across time and space.

Research from the 1918 influenza pandemic, including that by Chandra et al., suggests that even with a vaccine and with different levels and types of nonpharmaceutical interventions, it would be wise to prepare for (1) more infections and deaths in the short run as the Northern Hemisphere now is in the middle of the winter season and (2) later peaks and troughs or waves in 2021 and possibly in 2022. We also should be aware that these later waves could be as bad as or even worse than the earlier ones. Some of the hardest-hit areas in 1920 were isolated Indigenous communities that had avoided infection in 1918 and 1919. For example, urban and well-connected White majority populations in high-income Western countries in 1918 and 1919 had less than 1% mortality, whereas the Sami areas of Enare in northern Finland and Arjeplog in northern Sweden had 10% and 3% mortality, respectively, in their 1920 outbreaks.³

CONCLUSION

It has been said that those who forget their history are bound to repeat it. In 1918 and in 2020, quite a large proportion of both laypeople and those in charge of public health likely believed that (1) infectious diseases with the potential to cause severe pandemics belong to the past and that (2) medical problems during pandemics will be solved quickly by new technology and medical advancements. The 1918 influenza and COVID-19 pandemics have thus far shown us that these two beliefs were wrong.