I'd done research years ago for a friend of a friend. What I dug up didn't really sit well, given how many people had polio vaccines. Yes, the vaccine is great in that it kept people from getting polio, but there were varied effects on those who had it (and depending upon which version they had).
The virus conferred IgG mediated immunity into the bloodstream and is supposed to protect the motor neurons. MG is an "IgG" mediated immunity disease, whereas celiac disease, for example, is IgA. It's not a huge leap from there to conclude that the vaccine could potentially contribute to any number of neuromuscular diseases, including ALS.
There was both an oral and injectable version of the vaccine. The oral one sometimes caused a neurological infection and paralysis. Other vaccines, such as those for the flu, now have adjuvants such as squalene in them to "supercharge" the immune system to produce the antibodies. In those with an autoimmune history, that's not a great thing to have added to the body.
They added formaldehyde back in the flu vaccine last year. Oh, goodie.
The history of the polio vaccine is fraught with issues, such as the rhesus monkey kidney cells that were used to prepare the virus were found to have a virus (SV40) that was later shown to cause tumors. A person could do a thesis on the development of the vaccine alone.
If you have a history of immune issues in your family, or have a heritage which tends to acquire them (i.e., Northern European), then vaccines should always be thought of in that context.
There are so many factors that could make an immune system go haywire or that could contribute to a mother with a history of polio and PPS having a child with a NM disease. It's a guessing game, although I suspect someone out there knows the connection.
I'm glad your Mom enjoys a good life. I hope you do, too.
Annie