I have already thought about this. I got allergy shots when I was a kid, I "was" allergic to dust, and suffered from asthmatic bronchitis, my mother told me that I was not sick when I was born but after the first month she told me I almost die from asthma, guess what? I was vaccinated before that happened.
I don't have any idea of what exact treatment they gave me for bronchitis, but they were more shots for sure. I asked my mom about this, she doesn't know, it piss me off that getting vaccines when I was a child could have triggered this thing. But in the end I have many symptoms of low thyroid, I don't know the mechanism of how allergy shots or vaccines can cause hypothyroidism.