How to handle COVID-19 data in a panel I have panel data with COVID-19 variables starting in 2017 to look at how the pandemic affected stock markets. My N = 487 with 494500 daily observations. At the moment I left the time period before 2020 blank in the panel data resulting in my models only taking into account 151000 observations. Am I allowed to fill in the data period from 2017 to 2020 with 0's if I use the daily amount of new vaccinations and deaths to increase the amount of rows incorporated in the model?
Kind regards

Since you are interested in the stock market a more elegant way to incorporate the pandemic covariates would be to include a set of dummy variables (be aware of the dummy variable trap) and, depending on other independent variables you are considering, interaction terms of the pandemic dummy variables and other covariates. If you are dealing with daily data you may also consider to employ Chow test to determine whether there is a structural change between the two different periods.
I suggest you to have a look at Chapter 13 of Introductory Econometrics: A Modern Approach by Jeffrey Wooldridge.
