Thanks for commenting. Actually, yes, the 1918 influenza outbreak has been linked to an outbreak of Parkinson's disease years later. This article describes this well: https://www.parkinson.org/blog/science-news/flu

There's some causal evidence in animal studies too, where influenza infection can infiltrate the brain areas implicated in Parkinson's disease and produce symptoms of Parkinson's.

I've also written about it in an old Medium article of mine. It's my old work, so the quality may not be good hahaha. Link is here if you're interested: https://medium.com/microbial-instincts/how-the-flu-can-cause-parkinsonism-af807df5cad8?sk=8a129c4b2c4f017e0000d034989cdc01