IMHO, the immune system is vastly more complex than what is understood today. Although we do know that autoimmune diseases sometimes develop after certain infections (eg, strep) I believe that is a very incomplete picture. Our immune systems are shaped by all the cumulative infections, and related antibodies that are created, in our lives. The number of infections and antibodies are pretty much unique to each individual, and one would be surprised how many there are. For example, most of us have been infection with at least one strain of the herpes virus but are asymptomatic ... there are several strains of the herpes virus.
This points back to your vaccination comment. Since vaccines unnaturally "jostles" the immune system with foreign matter it can, in my opinion, tip one over to developing an autoimmune disease. Psoriasis sufferers can suffer flares upon receiving a vaccination.
So I agree vaccines are a contributing factor. Of course it is a risk-benefit decision on whether to get a vaccination. As an adult, and a Psoriasis sufferer, I personally choose not to get them.
PS - and certainly, when you add in heavy metal exposure from an early age it is easy to believe autoimmune diseases, such as Hashimoto's are far more prevalent nowadays.