“How does the above evidence rule out optionB?”
Children with a genetic predisposition despite having a higher rate of being diagnosed with autism, MMR shot did not play a factor, in fact, this specific group when vaccinated actually had a slightly lower rate of autism.
There are multiple studies that all conclude the same, groups that have not received the MMR shot have the exact same or very similar rate of autism. Receiving the MMR shot had no effect on being diagnosed with autism.
So if those with autism had “variable x” and the MMR vaccine together with “variable x” was the cause for the autism, this would mean that both groups, the vaccinated and unvaccinated would have a similar number of children with variable x, yet just the group that received the MMR vaccines would have children diagnosed with autism.
First off, at times this is a limitation of a retrospective study, you can always claim there were other unknown possible variables, however, in this case, this is not possible, as the autistic children actually had a lower vaccination rate.
The study took 95 thousand children, of those that were diagnosed with autism, they found no correlation between being vaccinated and not being vaccinated, no correlation between at what age the vaccine was given.