It's a factor now. Show me the study that proves that Prevnar13 doesn't cause autism.
Prove to me that pizza doesn't cause autism, until you can, that means that my assertion that pizza causes autism is valid.
You see why that doesn't work, right?
That's a strawman argument. Before I take a vaccine; I want to know what the risks are. I want to know who to sue when the product doesn't live up to the manufacturers claims. If I took multiple vaccines at same time; the manufacturer will try to blame his poisonous product on someone else's poisonous product.
What's worse is that our government has made it so that you can't even sue these corporations for selling you their snake oil.
It's not a strawman, it's what they're doing. If the original claim (that was started by Wakefield, and then adopted by people like RFK...and for the record, again, I like RFK, I think he's wrong about the MMR vaccine, but I like him. I think obesity is a bigger concern for our nation than measles or rubella) was that the MMR vaccine was responsible for an uptick in Autism, then the burden of proof is on the affirmative position.
You need to be able to demonstrate that the MMR vaccine increases that risk. Introducing new variables post-hoc that people haven't had time to study yet is a dishonest way to approach it.
For instance, if I made the claim "eating chicken is the reason for prostate cancer", and someone conducts a large-scale longitudinal study, and concludes, with or without chicken the in the diet, the prostate cancer rate is pretty much identical.
I can't come back and then say "well, you never studied it in a way that differentiated whether or not the chicken had paprika and bbq sauce on it, therefore, you can't tell me chicken is safe!"
But, all of the technical "debate-rule" jargon aside, for people who are staunchly anti-vaccine, there's literally no study, data point, etc... that can ever convince them otherwise on that particular topic. They've already got their conclusion, and then just introduce a variety of "what about" rationales into the equation.
Even if I could present them with study results that answer all of their hypotheticals, covered all their newly introduced variables, etc... they would just resort to "the study was rigged". As someone who grew up in an anti-vaccine household, I have more than just a little bit of experience debating anti-vaxxers.