Ask HN: Leading indicators for Covid-19 spread

Hi, I've built a small covid-19 model. Looking at the data for Germany, it is quite visible that the data seems to be offset by 9 days. E.g. a clear spike of new infections 9 days after new years eve. In my mind the chain is as follows: attitude change -> behaviour change (x days later) -> more new infections (x days later) -> officially reported new infections (9 days later) I would love to find some (publicly available) data source that I can use to model (one of) these leading indicators. If anyone has any ideas, I would be very grateful. Thank you!