We ( @Alex_Washburne and I) recently wrote about using influenza surveillance networks (which report influenza-like illness -- ILI) to track and understand COVID-19 in the US.
https://www.medrxiv.org/content/10.1101/2020.04.01.20050542v1

Below I share some new findings. (Thread)

Some hypothesized our ILI surge was due to fear (e.g., typical mild ILI is now more likely to get reported). We found NYC emergency departments suggest the opposite may be true. ILI admission rates have been increasing suggesting higher average severity of illness before.

In New York City it appears there is a relationship between age and the ILI surge in all 5 boroughs. (This year in red) past 4 years in grey. This is highly suggestive that the known biology of COVID is showing through in the ILI surge.

We also find evidence that the ILI surge may be an early predictor of COVID -- giving early warning early on and then predicting a decrease in new cases, deaths, and hospitalizations. ILI seems to lead deaths by approximately 5 days. (Data from NYC)