I feel the need to repost this from above....
Normally don't post often, but this one hits close. I am a pediatrician, researcher, and epidemiologist. There are some here that are using facts and critical thinking, and many that still are adhering to popular beliefs and misunderstanding what scientific research is all about. A few things to consider:
1) Science is not about proving anything 100%. By nature, that is impossible. Can we ever prove that vaccines absolutely do not contribute to to autism? No. Only if we studied all 6+ billion people on Earth could that be possible, and even then, it would not account for the multi-factorial (epigentics as someone above pointed out) nature of many diseases. Using the best science and nearly 100,000 children, the link with a high degree of certainty minimizes the risk of autism from vaccines
2) Surveillance Bias. Do you know why more kids have autism? In part its because our generation of parents looks for any signs of imperfection, or not "competing" with other young children. They alert the primary doctor, who now also has a bias towards diagnosis. Bam...you child has autism-spectrum disorder. I am CERTAIN that MANY people in previous generations have ASD but were not diagnosed. Why? Because nobody was looking for it. Many of my teachers in med school and since have some ASD, I am sure of it. It was just not en vogue to diagnose. Also, ASD seems to have a tendency for more wealthy Caucasian populations, of which there are many more in the US now that 30+ years ago. This may go hand in hand with increased surveillance.
3) Time of Diagnosis. It is in many ways coincidence when ASD is diagnosed, as it is during the age that many vaccines are administered (from 1-4 years of age). The chance of diagnosis of Autism is most likely to be in this window, which makes me think the chicken (autism) came before the egg (vaccines) in most cases. In terms of time, also note that the agent thought to contribute, Thimerisol, has bee absent in vaccines for 15 years.
4) Societal Benefit. People who refuse to vaccinate based on hearsay are the most selfish in the world. They depend on others who are vaccinated to protect their children. They use idiots like Jennie McCarthy and Facebook moms to make their conclusion. Vaccines save lives. Vaccines have probably saved your life, you just take it for granted. I have seen infants die of pertussis (whooping cough), children die of measles, pneumococcal, and Hib sepsis, and have seen the torture suffered by an 8 yo with tetanus. The number of adverse events from vaccines compared to the number of people protected is miniscule. They put young infants, children with cancer and other immune suppressed at risk because of your selfishness. Every time I see a child diagnoses with a vaccine-preventable disease, it makes me cringe. Do you all know why child mortality from infection is so rare in the United States? Because we vaccinate. It is not voodoo, it is common sense.