April 7, 2006 -- Debate over a possible tie between mercury-containing vaccines and autism flared up this week as activist groups launched a campaign accusing federal health agencies and prominent researchers of manipulating scientific findings on the link.
Some parents of autistic children have long blamed vaccines containing the preservative thimerosal for an alarming rise in the disorder. Thimerosal contains a type of mercury. A series of reports by the Institute of Medicine (IOM) ending in 2004 concluded no evidence could be found linking the vaccines to neurological diseases, including autism.
But groups this week mounted a campaign to publicize previously undisclosed transcripts and emails that they say point to efforts by the CDC to manipulate the IOM's scientific conclusions on the safety of vaccines containing thimerosal. The groups accuse the CDC of trying to defend a long-held policy promoting childhood vaccinations.
"In the interest of protecting the immunization program, they forgot about child safety. They are continuing that pattern of behavior and denial that thimerosal causes harm," Bobbie Manning, vice president of Advocates for Children's Health Affected by Mercury, tells WebMD.
According to the CDC, all vaccines recommended for children are available in thimerosal-free versions. But some parents say millions of previous exposures helped caused a spike in autism cases since the 1980s.
The CDC contracted with the IOM in 2001 to generate a series of reports on possible links between vaccines and a variety of health problems. An IOM committee of outside experts, led by Harvard researcher Marie McCormick, MD, found no evidence of a link and concluded that proposed biological explanations for a mercury-autism relationship were "theoretical."
Allegations of Bias
Activist groups released transcripts of closed-door conversations in 2001 between McCormick and Kathleen Stratton, the study director. Groups say the conversation suggests that the committee would fashion its findings to meet the CDC's desires to play down a link between thimerosal and autism.
"[The CDC] wants us to declare, well, these things are pretty safe on a population basis," McCormick said to Stratton, according to the transcript, posted on a web site called Putchildrenfirst.com.
Thirty-four pages later in the transcript, McCormick states, "...we are not ever going to come down that [autism] is a true side effect."
Manning said the transcript shows that the CDC "directed that committee to find what they wanted to find, which was no causation" between vaccines and autism.
In an interview, McCormick confirmed that the statements in the transcript are "accurate and true." But she said there was "no truth" to allegations that CDC officials influenced the IOM or that the committee reached conclusions before its scientific review.
McCormick said her comments reflected a debate over whether the committee would look at vaccine effects in individuals or across populations, and not what any specific findings would be.
The conversation also took place in late 2001, before the committee's final 2004 report on vaccines and autism was planned, McCormick said.
"In 2001 we did not know we were going to look at autism again. To use those as evidence for what we did in 2004 is really inappropriate," she said.
McCormick added that the committee's experts were chosen specifically for their scientific independence and for a lack of ties to both pharmaceutical manufacturers and the CDC.
Parents groups alleged that CDC officials had worked to dissuade agency scientists from looking more deeply into links between thimerosal and autism.
The groups also alleged that CDC officials narrowed the scope of the IOM's report to include a handful of studies, most of which the agency had a role in funding or planning. Those studies generally showed little evidence of a link between vaccination and autism.
Tom Skinner, a CDC spokesman, said the agency has been "very transparent" about its ongoing studies of autism and vaccines and that the emails have been taken "out of context." He said the agency closely guards its scientific credibility and "in no way" tried to influence IOM experts.
"We stand behind our science that's been done to this date and we will certainly do more in the future," he said.
Louis Z. Cooper, MD, an emeritus professor of pediatrics at Columbia University and a founder of the National Network for Immunization Information, said in an interview that some of the emails and transcripts "cause some anxiety" because they may help fuel fear among parents about the safety of vaccines and the motivations of health officials.
Still, Cooper, who noted he's known McCormick professionally for at least 20 years, called accusations of bias against her or other members of IOM's committee "rubbish, scurrilous, and awful."
"If I wanted a group who were committed to objectivity and were committed to science, I couldn't have asked for a better group of people," said Cooper, a former president of the American Academy of Pediatrics.
Manning said her group and others would continue to push for congressional investigations into how the IOM conducted the studies and whether they were influenced by the CDC. "We believe that this is a serious issue that needs to be examined," she said.