I suspect that the primary reason that people catch more colds in the Winter in Northern climates is because the sun hits BC at an angle in Winter. This filters the UVB rays that turn 7-dehydrocholesterol into vitamin D.

Since the various forms of vitamin D control the immune system, people have weaker immune systems.

I don't when private institutions require people to wear masks in doors. I get ticked when they force people to wear masks outdoors in public places.