There was some interesting research out of the Karolinska Institute showing people had a response to the virus from their T Cells without developing antibodies. They reckon lots of people might have had it without knowing and had a T Cell response to the virus, which also might explain why results from these antibody studies are so low. They tested asymptomatic family members of people who had antibodies and the family members didn’t have any antibodies, but they had a T Cell response indicating they had the virus at some point. The effectiveness of T Cells diminishes the older you get which also might explain why younger people are mostly unaffected.
I reckon the more research that’s done into Covid-19 the more we’ll see it’s mostly harmless (obviously not harmless but similar to the flu).