I think you’re right.
There was a time that they were using peanut oil as a base for many of these shots. Voila.....peanut allergies in so many! Deadly allergies, as well. When I went to school, peanut allergies, or any allergies, for that matter, were unheard of.
I did some research 38 years ago (the old fashioned way lol - sending away for articles, books in the mail) and became an avid anti-vaxer way back when. I just couldn’t see sticking that stuff in a healthy baby....it made no sense. Thankfully none of my grands got any shots either.