The variant and people letting down their guard now that their most-vulnerable loved ones are vaccinated, plus the natural impact of winter habits moving all socialization, dining, sports, etc. indoors. And we've had more school/sport related clusters than at any previous phase of the pandemic. We got through HS football season without many sport-related outbreaks and I think people were seriously underestimating how much worse basketball is in terms of facilitating contagion. The indoor/outdoor difference still isn't getting talked about nearly enough IMO.
Back to and in some cases above fall level in numbers, but not severity, at least so far. Many occupied beds but fewer of them in ICUs and fewer needing ventilators. So at this point, it is a strain but not as dire as in our fall surge.
Part of it is that we did it so much better for the first year, which means we had a LOT more people walking around with no immunity whatsoever when the more contagious variants started spreading. Even though natural immunity appears to be imperfect and perhaps shorter lived than vaccine-induced immunity, it does offer a large degree of protection when compared to no immunity at all. In Feb, Michigan was 44th of 50 states in cumulative case rates with 30-40% fewer cases per million than states like Texas and the Dakotas. So we were essentially in the same place this March when the variants started spreading as we were last March when the novel virus started spreading for the first time, with the vast majority of people having absolutely no immunity at all.
It is amazing how little people think about the proximity to Canada as a factor (and Ontario's proximity to us as a factor in their case trends). I just read an article in one of my news apps that was from the LA Times, talking about MI vs. CA trends, and it mentioned and then dismissed as probably not being much of a factor because "the border is closed". Yes, the border is closed... but only to non-essential travel. MDOT figures indicate a 35-40% reduction in volume at our major crossings. The other 60-65% is essential and still flowing, which is a lot of opportunity for the virus to hitch a ride. But the economies of neighbor cities like Detroit & Windsor are so interconnected that there's no way to actually close the border. My kids have had Canadian classmates, my mom had Canadian coworkers when she worked in Detroit, my husband's plant sends parts to assembly facilities in Canada, etc. So even with the border ostensibly closed, our covid destinies are very much intertwined.