There are a lot of factors contributing, in particular the age distribution of those people getting infected.
One thing is "viral load", which has to do with how much of the virus is present at initial infection. Because immune system response takes time to ramp up, e.g. 10x more virus in the beginning means that it can do much more damage before the immune response. It's likely that social distancing and masks have reduced the average viral load at infection time.
One thing is "viral load", which has to do with how much of the virus is present at initial infection. Because immune system response takes time to ramp up, e.g. 10x more virus in the beginning means that it can do much more damage before the immune response. It's likely that social distancing and masks have reduced the average viral load at infection time.