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Death curves in Philadelphia and St. Louis during 1918 Spanish flu pandemic (panel A, adapted from Hatchett RJ, et al. Proc. Natl. Acad. Sci. U. S. A. 2007; 104, 7582-7587) and curves of seven-day rolling average of newly confirmed COVID-19 cases in the US (red) and EU (blue) (panel B, Johns Hopkins Coronavirus Resources Center, https://coronavirus.jhu.edu).
