I don't think it actually changed as much as you are implying it did. Some studies of infection in the general population have indicated that infection rates we

I don't think it actually changed as much as you are implying it did. Some studies of infection in the general population have indicated that infection rates were much higher than estimated, but some of those studies were rushed and haven't held up well. I remember some earlier ranges that said it could be as high as 3-5%, but mostly it has stayed around 1% and that fell significantly after the vaccine. I mean, if we assume that every single person in the US has been infected already with COVID, that puts the death rate at 0.2% and without a vaccine, it would have been a lot higher.