An old complaint about the safety of childhood vaccines is finding new life at the United Nations.
The U.N. Environment Program is considering a ban on thimerosal, a vaccine preservative that is widely used in developing countries. The program expects to make a decision sometime after a final meeting on the issue in January.
Thimerosal, which contains a form of mercury, was removed from most childhood vaccines in the U.S. and Europe more than a decade ago, amid public fear that it could cause autism. Several large studies later found no risk from the preservative and that removing it did nothing to change autism rates.
Now the proposal before the U.N. has public health officials once again trying to reassure people that thimerosal is safe. Three separate papers in the journal Pediatrics argue against an international ban.
"This is critical," says Dr. Walter Orenstein of the Emory Vaccine Center at Emory University, and an author of one of the papers. "Lives potentially would be lost if we banned thimerosal from vaccines."
Thimerosal keeps vaccines from going bad in parts of the world where other options, such as refrigeration or single-dose vials, aren't practical.
The proposed ban is part of a larger effort to reduce exposure to mercury, which can affect brain development. And public health experts strongly support most aspects of that effort, Orenstein says.
"But when it comes to thimerosal in vaccines, the benefits far outweigh any risks," he says, adding that a ban could mean the return of diseases that used to kill millions of children each year in developing countries.
"Pertussis or whooping cough could really resurge in these areas," Orenstein says.
But Orenstein and other experts weren't always so certain about thimerosal. In 1999, they asked vaccine makers in the U.S. to stop using the preservative in childhood vaccines.
At the time, some parents of children with autism were alleging that the thimerosal in vaccines caused the disorder. Also, researchers realized that some children could be getting more mercury from vaccines than the Environmental Protection Agency deemed safe.
So Orenstein says he and others erred on the side of caution.
"At the time, we just didn't know what the toxic effects might be or might not be," he says. "And one of our concerns was, what if we did the studies and three years later found there was harm?"
The studies showed just the opposite, though. And scientists also determined that the form of ethyl mercury in thimerosal is far less dangerous than methyl mercury, the form found in seafood. So the EPA exposure limits didn't really apply.
But groups opposed to thimerosal say they're not convinced by the studies. And they say it's wrong to give the preservative to children in developing countries, but not to children in the U.S. and Europe.
The practice is "egregious, offensive and unacceptable," says Eric Uram, executive director of the U.S.-based group SafeMinds.
SafeMinds has played a prominent role in pushing for the international ban. But so far, countries that might be affected by it have been less vocal.
Uram says SafeMinds has contacted officials from countries including Nigeria and Uganda and found they are concerned. But he says they are hesitant to speak up because the World Health Organization has deemed thimerosal safe.
"They defer to WHO for guidance on health issues," he says. "So it becomes inappropriate for them to say that the WHO is incorrect."
Uram also disagrees with public health officials who believe the ban would disrupt vaccination programs in developing countries. The ban would be phased in, he says, giving countries time to find alternatives to thimerosal.
But right now there is no good alternative, says Heidi Larson of the London School of Hygiene and Tropical Medicine. In the U.S., she says, most childhood vaccines are packaged in single-dose vials, which don't need a preservative. That drives up the cost of each dose and makes it more difficult to transport large amounts of vaccine, she says.
Also, Larson says, there is no scientific reason to ban thimerosal from vaccines. "It would be bowing to public pressure," she says.