In 2011, the Coalition for Mercury-Free Drugs (CoMeD) released documents obtained through a Freedom of Information Act request that raised questions about the CDC’s handling of a Danish study on Thimerosal — a mercury-based preservative used in some vaccines — and its potential connection to autism rates.
The Danish Study and Disputed Findings
The controversy centered on a study published in 2003 in the journal Pediatrics examining autism rates in Denmark following the country’s removal of Thimerosal from vaccines. According to CoMeD, the original data showed a decline in autism rates after Thimerosal was eliminated. However, the version ultimately published in Pediatrics reported the opposite conclusion: that autism rates had increased after the preservative was removed, suggesting no link between Thimerosal and autism.
CoMeD alleged that CDC officials removed significant portions of the original data set and reinterpreted the remaining figures to support a conclusion that contradicted the raw data.
Allegations of Data Manipulation
The FOIA documents purportedly showed that the study’s original authors contacted CDC officials after submission to flag what they described as incorrect interpretations of their data. According to CoMeD’s account, the CDC acknowledged the concerns but proceeded to push the altered version through an expedited peer review process at Pediatrics, where it was ultimately published.
CoMeD called for a full criminal investigation into whether scientific fraud had occurred, along with a retraction of the published study. “This should not be tolerated by those who are entrusted with our children’s health and well-being,” said CoMeD president Lisa Sykes.
The Broader Thimerosal Debate
Thimerosal had been used as a preservative in multi-dose vaccine vials since the 1930s. It contains ethylmercury, which the body processes differently from the methylmercury found in contaminated fish. In 1999, as a precautionary measure, the U.S. Public Health Service and the American Academy of Pediatrics recommended removing Thimerosal from childhood vaccines, and manufacturers largely complied by 2001.
Multiple large-scale epidemiological studies conducted in several countries have examined the question of Thimerosal and autism. The scientific consensus from organizations including the World Health Organization, the Institute of Medicine, and the European Medicines Agency has been that the available evidence does not support a causal link between Thimerosal-containing vaccines and autism.
Transparency and Public Trust
Regardless of where one stands on the underlying science, the allegations raised by CoMeD highlighted a persistent concern: the importance of transparency and data integrity in public health research. When regulatory agencies are perceived as influencing study outcomes — whether the perception is justified or not — it erodes public confidence in the institutions responsible for vaccine safety decisions.
The episode became part of a larger ongoing debate about vaccine ingredient safety, regulatory accountability, and the public’s right to access unaltered research data used to inform health policy. Critics of the CDC’s handling argued that institutional credibility depends on allowing data to speak for itself, even when the findings are inconvenient.
