I think it would be moslty the new variant and then the Christmas effect which caused the steepest rises and the most dangerous because the deaths didn't really start climbing until just before Christmas and then sadly after, as we know, they shot up. Christmas shopping in the weeks leading up too Christmas day too
Children, especially primary, and their parents are not generally the most at risk. So even if infections went up slightly in September, this does not mean deaths and hospitalizations did in relation to that. That's what's important.
Deaths were still in the low hundreds a day at the end of October. They didn't start going up until November and December and then, sadly as we know, really shot up in January