It looks exponential. And as soon as nature is involved, it is exponential anyway. The lockdowns have been so hard because they should break down exponential behavior. I think there are websites on which you can calculate SIR models. Have a look at https://www.physicsforums.com/threa...th-and-other-curiosities.970262/#post-6164027
Yeah, we know infectious disease follows an exponential curve always. However, data may not accurately reflect the curve, or may come in delayed, or vaccine efforts may blunt the effect and may make it look quadratic.
I think paper discusses these issues better and shows where sometimes a quadratic model comes out of the data: