I wish you good luck, as 99.99% of the anecdotal claims out there that conclude vaccination is bad are based on unfounded rumors.
Note that much of the negative public opinion is based on a fraudulent (and retracted) paper by _Wakefield in The Lancet (1998)_. Unfortunately for you, however, it is in English.
My French is a bit rusty, but if you go to Google Scholar and type in a search term like **vaccination results in autism** ( _les résultats de la vaccination dans l'autisme_ ) or _Wakefield vaccination autisme_ something might pop up in French that advocates against vaccination.