One variable may be Vitamin D. It was a warmer Autumn than usual throughout all of New England but was more so in southern New England. So people in southern New England were likely outside more than people in northern New England until very recently. That means people in southern New England received more Vitamin D from sunshine and were also indoors less which would also decrease transmission.Of course this variance in Vitamin D and being indoors more during colder times is what drives seasonality.