This study reports results on the younger siblings of autistic older siblings. Thus there is an obvious confounder in that parents of younger siblings who observe that the MMR vaccine visibly caused the autism of the older sibling will almost certainly withhold the vaccine from the younger sibling. In fact, there are a large number of anecdotal reports of precisely that: parents who say that within minutes or days of receiving the MMR vaccine, their child who had been normal became autistic. The study reports that MMR is protective against autism in the oldest age group by almost a factor of 2. (The result is barely not significant, but is nonetheless highly suggestive.) The most straightforward explanation for this is that the MMR causes autism in some genetically susceptible individuals, and when it does it does so in a way that is visible to the parents who then withhold it from the younger siblings. So the younger siblings of autism victims who do not get the MMR vaccine also are highly likely to be genetically susceptible to get autism, whereas the younger siblings of autism victims who are given the MMR vaccine by their parents are not as likely to be genetically susceptible. It is unclear why one would craft a study with such an obvious confounder.
Note that there is a repeated finding that early Thimerosal is significantly preventative of general developmental disorders, unspecified developmental delay, and attention deficit disorder (Andrews et al) and ASD(Price et al.)
This tends to confirm the hypothesis that the protective effect consistently observed in these three experiments is an artifact of parents observing damage in their children, and suspending or delaying further vaccines, thus putting high risk or ASD kids into the "low vaccine" or "low thimerisol" pool.
Nick Andrews; Elizabeth Miller; Andrew Grant et al, Thimerosal Exposure in
Infants and Developmental Disorders: A Retrospective Cohort Study in the United
Kingdom Does Not Support a Causal Association, Pediatrics September 2004,
VOLUME 114 / ISSUE 3
Cristofer S. Price, William W. Thompson, Barbara Goodson,et al, Prenatal and
Infant Exposure to Thimerosal From Vaccines and Immunoglobulins and Risk of
Autism, Pediatrics October 2010, VOLUME 126 / ISSUE 4