Hunch Looked, found nothing AD 1920

Sleepy sickness follows flu waves by about a year (Ravenholt and Foege)

Tested 25 October 2026 with US national annual death rates (scripts/el_flu.py). Year-to-year changes in encephalitis deaths do not follow changes in flu deaths a year earlier (1922 to 1938: r = -0.01). Caveat: Ravenholt and Foege used month of onset for 142 Seattle cases; national annual deaths blur a 12-month lag. England and Wales 1921 to 1937 agree: encephalitis one year after flu, r = -0.26 (the wrong direction).

How it connects

This hunch is about What caused encephalitis lethargica, the 'sleepy sickness' of 1917 to 1928?

This hunch 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 hunch we read it in Ravenholt and Foege 1982, 1918 influenza, encephalitis lethargica, parkinsonism, Lancet 2:860 (Seattle-King County monthly data)

This hunch is argued against by US death rates 1910 to 1938: encephalitis did not rise in 1918; it peaked in 1920 and 1923 no one-year lag in national data

This hunch is argued against by England and Wales 1919 to 1937: sleepy sickness peaked in 1924 (5,039 cases), not after the 1918 flu no one-year lag in England and Wales

This hunch is argued against by Scotland 1921 to 1937: sleepy sickness peaked in 1924 and did not follow the flu years no one-year lag in Scotland

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