Covid-19 is not a strain of the flu. It’s an entirely new version of the corona-type virus first identified in the 1960s and a new disease. Flu is caused by evolutions of RNA-type viruses. Both are respiratory infections, however. It progresses differently, too. As James mentioned above, it appear to be biphasic, which basically means you feel better, then you get worse again.
https://www.statnews.com/2020/03/03/who-coronavirus-different-than-influenza-can-be-contained/