What is Simpsonwood?

Believe it or not, a twenty-some-year-old rumor that a secret CDC meeting was held to figure out how to hide the harms of thimerosal in vaccines is still trending.

Over the years, scientists have carefully studied vaccines to make sure they are safe. One topic that often comes up is thimerosal, a preservative that was once used in some vaccines. Thimerosal contains ethylmercury, which is not the same as the harmful mercury called methylmercury that can be found in some fish. Ethylmercury leaves the body quickly and has been used safely since the 1930s in vaccines, medicines, and contact lens solutions.

In 2000, the Centers for Disease Control and Prevention (CDC) held a two-day meeting at the Simpsonwood Conference Center. The purpose of the meeting was to review early data from the Vaccine Safety Datalink. Scientists wanted to see if there might be any link between thimerosal and neurological problems in children. The meeting included experts from public health groups, universities, and vaccine companies. It was a normal scientific meeting where researchers discussed data and asked questions.

Years later, the meeting became a focus of the anti-vaccine movement. In 2007, the U.S. Senate HELP Committee reviewed these claims. The committee found that the accusations had little or no truth. They concluded that the CDC did not interfere with studies, did not pressure scientists to change results, and did not hide data. Claims that the meeting was meant to cover up a link between vaccines and autism were also not supported by evidence.

Since then, many large studies have been done. These studies show that thimerosal does not increase the risk of autism. In fact, thimerosal was removed from routine childhood vaccines in the United States by 2001. Even after its removal, autism diagnosis rates continued to rise. This shows that thimerosal was not the cause. The increase in diagnoses is mostly due to better awareness, improved screening, and changes in how autism is defined.

Scientists now know that autism is linked to genetics and brain development before birth, not vaccines. Research has also found that brain differences related to autism begin during pregnancy, long before any childhood vaccines are given.