There is no evidence of the link between sleeping sickness, EL, and Spanish flu.

> Since encephalitis lethargica’s (EL) prevalence in the 1920s, epidemiological and clinical debate has persisted over whether EL was caused by, potentiated by, or merely coincident with the Spanish influenza pandemic. Epidemiologic analyses generally suggest that the disorders were coincidental.

https://en.m.wikipedia.org/wiki/Encephalitis_lethargica https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2778472/

There is nothing to play down. More than a year into the pandemic are there is still no evidence of long-term damage except in rare cases. Evidence of inflammation in monkeys does not qualify, before you ask.