Good question. I was hospitalize with, what the docs said, was walking pneumonia at the end of October, 2019. It had all the symptoms of COVID including the possible need for a ventilator (and possible death).
Later, I learned that COVID may have been present in the US prior to December, 2019. I asked my doctor if that was a possibility as I wanted to donate plasma to help others. He said no but, no COVID test was done. So, I have stayed in my home for the most part of last year (and so far this year). Not taking any chances and awaiting my second shot.