Not clear what you are seeing in these graphs, but if its the regular weekly slight drop in numbers, its going to be a weekend effect, when some parts of the testing-clinical care-reporting chain have a few well-deserved days off. Its often matched by a slight boost on the following two days when they catch up on the data.
Its why the more useful reporting uses a 7 day running average to smooth out daily peaks and troughs that have less to do with the disease than the people managing it.
But, if you have another pattern in mind, please ignore my Dopesplaining and expand your thoughts.
Yes, what Banksiaman says – I believe this is universally expected and accepted. I think it’s mostly got to do with when the reporting happens, but there could also be some cycling in actual medical status itself, too, as so many human phenomena depend at least a tiny bit on our weekly schedule shifts.
I posted this story on another website, which has some people there who know way more about this than I do, and several of them pointed out the same thing - that it’s more about reporting than actual incidence. The pattern was still incredibly consistent, which was why I posted it here.