

That is a relatively new vaccine. In the US, that’s part of what you get as a kid now (not going to fact check the current guidance cause im afraid to look), but if you’re old enough to have actually gotten chickenpox, you likely havent gotten the vaccine unless you asked for it.
In my experience in the US, it seems like Dr’s dont really keep up with recommendations once you are over 18.

Most ALS is not genetic, and im not sure about parkinsons, but I suspect it’s similar. Lots of studies these days are finding links between viruses that dont actively cause much harm when you are infected, but and up being highly associated with autoimmune diseases. A prime example is Epstein-barr virus and MS. I have no clue what the mechanisms are, and im sure scientists are still learning, but basically an infection could cause an immune response that is too strong, and even after the infection is gone, the response remains.