Regarding China and their possibility for a second viral wave, I will tell you that I was in Western China in 2008 when I adopted my daughter, and found it odd that, even then, a good 30% of the people there walked around wearing a mask. I found this in a few major cities, and reconciled it as a way to protect themselves from pollution, which was heavy in their large cities. However, I was told by one of the hotel staff that though pollution was a factor in those choosing to wear masks, that even then, some people there feared the possibility of a pandemic due to the heavily populated areas.
That said, if that trend continued (I haven't been back, but I loved China and would go again in a heartbeat) I could only assume that a second wave there might be mitigated compared to one here. I had yet to see this practice in any US city, notwithstanding the occasional mask-wearing person in NYC and Philly.