Clue from nature AD 1920

US death rates 1910 to 1938: encephalitis did not rise in 1918; it peaked in 1920 and 1923

Linder and Grove 1943, Table 12, per 100,000. Influenza: 1917 17.4, 1918 301.8, 1919 99.0, 1920 70.5, 1921 11.3, 1922 31.0, 1923 44.1, 1924 19.0, 1925 29.1, 1926 40.0, 1927 22.3, 1928 44.8, 1929 55.1. Encephalitis: 1917 0.8, 1918 0.8, 1919 1.5, 1920 2.4 (all encephalitis), then lethargic encephalitis 1921 1.5, 1922 1.3, 1923 2.0, 1924 1.4, 1925 1.6, 1926 1.4, 1927 1.2, 1928 1.2, 1929 1.1, 1930s 0.7 to 0.9 (1933 1.1 is the St. Louis encephalitis outbreak, a different virus).

How it connects

This clue from nature argues against Sleepy sickness follows flu waves by about a year (Ravenholt and Foege) no one-year lag in national data

This clue from nature supports this hunch Sleepy sickness and flu rise in the same years modest same-year co-movement

This clue from nature is a clue for What caused encephalitis lethargica, the 'sleepy sickness' of 1917 to 1928?

This clue from nature we read it in Linder and Grove 1943, Vital Statistics Rates in the United States 1900-1940 (US Census Bureau), Table 12: crude death rates for each cause. Values read by eye into el/us_rates_1910_1938.csv

This clue from nature came from this step Read US death rates by cause 1910 to 1938 and tested sleepy sickness against flu