Having to wash your hands every day until you die? Sounds like the optimal solution for pharma companies, a consistent and never ending stream of income from handwash.

Wait until you hear about food and water.

Food and water aren't as easy to restrict as medicine of any kind. Just think of the patents, with the right tricks they could even half ass the first version and patent every individual improvement over decades.

Probably not, unless you go back and forth between hemispheres so you are almost always in the colder season. Current flu vaccines only last a few months already, but flu is seasonal.