Officials at the Centers for Disease Control and Prevention (CDC) conspired to cover up information linking vaccines to developmental disorders in children, organizations representing parents of autistic children allege.

The advocacy groups have long contended that mercury and a mercury-based substance called thimerosal, which were commonly used as preservatives in vaccines, cause some children to develop autism or similar disorders.

The autism groups sponsored a full-page ad in today’s USA Today that reads, “If you caused a 6,000% increase in autism, wouldn’t you try to cover it up, too?” The ad alleges that the CDC “knows that the ambitious immunization schedule begun in the 1990s, nearly tripling the amount of mercury injected into our children, created an epidemic of autism in America.”

The organizations are holding a rally and press conference this morning to highlight their charges. Reps. Dan Burton (R-Ind), Dave Weldon (R-Fla.) and Carolyn Maloney (D-N.Y.) are scheduled to speak at the event in the park next to the Russell Senate Office Building.

The CDC, other federal authorities and even the American Academy of Pediatrics contest this theory and say there is no scientific evidence that vaccinations contribute to autism. Federal authorities also argue that the benefits of immunization against diseases such as mumps outweigh the risk of vaccines.

Autism groups say that one out of every 166 children has an autistic disorder. The CDC’s website says, “While it is clear that more children than ever before are being classified as” autistic, the agency does not know why, nor does it know exactly how many children have autistic disorders.

Based on internal e-mails written by officials at the CDC, the Food and Drug Administration (FDA) and others, the parents groups contend that federal authorities knew the vaccines were causing autism but failed to act.

Generation Rescue, one of the parents groups, has posted the documents on the website www.putchildrenfirst.org. Generation Rescue obtained the documents via the Freedom of Information Act.

“These are our federal health agencies that we trust … and they’re poisoning us,” said Wendy Fournier of the National Autism Association. “They’ve poisoned an entire generation of children,” she said. The CDC spearheaded an aggressive push to expand childhood vaccinations in the early 1990s.

Burton seconded the accusations in a statement yesterday. He has been relentless in his criticisms of the health agencies.

“I truly feel that the HHS [Department of Health and Human Services], CDC, [the Institute of Medicine] and the FDA have deliberately misled the American public on the dangers of mercury in vaccines, and I wholeheartedly support a thorough and independent investigation into the evident link between mercury and autism,” Burton said.

The CDC denied any cover-up and defended its policies. “We’ve taken this issue and the concerns very seriously from the beginning,” said CDC spokesman Glen Nowak.

The allegations of a conspiracy represent an intensification of a years-long campaign by these organizations.

The groups want Congress to investigate and will demand that criminal charges be brought against officials involved. The Senate Health, Education, Labor and Pensions Committee is investigating the agencies, a spokesman for the panel said. Last July, parents groups recommended to the committee that HHS, CDC and FDA officials should be charged with criminal negligence and criminal obstruction of justice.

In addition to the National Autism Association and Generation Rescue, A-Champ, NoMercury, Moms Against Mercury and AutismOne organized the rally and press conference. Today’s press conference will be followed by a conference on autism issues that will run through Monday.

Maloney said the agencies should respond better to the concerns of these parents and Congress but stopped short of endorsing the allegations of a cover-up.

“When it comes to mercury, autism and the government’s response, there are still more questions than answers. … I know that there are some in Congress who want to work to get those answers,” she said.

“While I cannot answer the question of an alleged cover-up, it is obvious to even the casual observer that the CDC has failed miserably investigating this matter,” Weldon said.

The organizations representing parents of autistic children have been vocal and aggressive in their campaigns to get mercury and thimerosal removed from all vaccines and to get the CDC and other agencies to change their policies related to childhood vaccines.

Their strategies have attracted the interest of many members of Congress over the years, notably Burton and Weldon. The conference report that accompanied the appropriations bill that funds HHS this year includes a provision requesting another study on the issue by the National Institutes of Health.

A scientific review issued by the National Academies’ Institute of Medicine in 2004 was intended to put the question of mercury and autism to rest but served only to fuel the fire.

The institute’s panel concurred with the CDC position. “Neither the mercury-based vaccine preservative thimerosal nor the measles-mumps-rubella (MMR) vaccine are associated with autism,” according to the press release that accompanied the report.

The parents groups alleged that the CDC pressured the committee that carried out the review to support its policies.

The chairwoman of the panel rejected that charge, which she characterized as an explicit attack on her integrity. Asked if CDC officials attempted to sway the committee’s deliberations, Harvard School of Public Health professor Marie McCormick said, “Absolutely not.”