Hunch Looked, found nothing AD 1923

Sleepy sickness and flu rise in the same years

Tested 25 October 2026 in two countries (scripts/el_flu.py). United States 1922 to 1938: same-year changes move together modestly (r = +0.43, p 0.03), but encephalitis rose in only 2 of 6 big flu years, and not at all in 1918. England and Wales 1921 to 1937: no link (r = +0.07, p 0.4); the 1924 epidemic came with a flu rise, but the big flu years 1922, 1927, 1929 and 1933 brought no rise in sleepy sickness (3 of 7 big flu years up). The US link does not replicate, so it is probably chance or a US certification habit. Scotland 1922 to 1937 agrees: r = -0.23. Three countries, one weak positive (US) and two nulls.

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 McCall, Vilensky, Gilman and Taubenberger 2008, The relationship between encephalitis lethargica and influenza: a critical analysis, J NeuroVirology 14:177

This hunch is supported by US death rates 1910 to 1938: encephalitis did not rise in 1918; it peaked in 1920 and 1923 modest same-year co-movement

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 same-year link 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 same-year link in Scotland

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

This hunch came from this step Tested sleepy sickness against flu in England and Wales