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And we're going to consider now another aspect of childhood health. An old complaint about the safety of childhood vaccines is finding new life at the United Nations. A branch of the U.N. is considering a ban on a vaccine preservative that is widely used in developing countries. This preservative contains a form of mercury.

NPR's Jon Hamilton reports it was removed from most childhood vaccines in the U.S. and Europe more than a decade ago, despite a raft of studies that found no risk.

JON HAMILTON, BYLINE: The preservative is called thimerosal and it keeps vaccines from going bad in parts of the world where other options, like refrigeration, would be difficult.

Walter Orenstein is from the Emory Vaccine Center at Emory University.

WALTER ORENSTEIN: Lives potentially would be lost if we banned thimerosal from vaccines.

HAMILTON: The proposed ban is part of a larger effort to reduce exposure to mercury, which can affect brain development. Orenstein says public health officials support most aspects of that effort.

ORENSTEIN: But when it comes to thimerosal in vaccines, which protect the vaccine supply in developing countries, the benefits of that far outweigh any risk.

HAMILTON: Orenstein helped write one of three papers in the journal Pediatrics that support continued use of the preservative. He says a ban could mean the return of diseases that used to kill millions of children each year in developing countries.

ORENSTEIN: Pertussis or whooping cough could really resurge in these areas. An organism called Haemophilus influenza type B, or Hib, which causes severe meningitis and pneumonia, that would resurge; Hepatitis B could go way up.

Orenstein wasn't always so sure about thimerosal. In 1999 he and many other experts asked vaccine makers in the U.S. to stop using the preservative in childhood vaccines. The move came amid public fears that vaccination could cause autism. There was also evidence that some children could get more mercury in vaccines than the EPA recommends. 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. And one of our concerns was: What if we did the studies and three years later found there was harm? Since that time, many, many studies have been done and we've learned a lot.

HAMILTON: Big studies in the U.S. and Europe found no risk to kids. And scientists determined that the form of mercury in thimerosal is far less dangerous than the form found in, say, seafood. So the EPA exposure limits didn't really apply. Even so, vaccine makers kept thimerosal out of childhood vaccines in the U.S. and Europe. And now, groups that still see a link between mercury exposure and autism are saying it's wrong to take a different approach in other countries.

Eric Uram is with the U.S. group SafeMinds.

ERIC URAM: SafeMinds saw this as an egregious, offensive and unacceptable outcome that was being foisted onto the developing world.

HAMILTON: Uram says his group contacted officials from countries including Nigeria and Uganda and found that they are worried. But he says they are hesitant to speak up because the World Health Organization has deemed thimerosal safe.

URAM: They defer to WHO for guidance on health issues. So it becomes inappropriate for them to say that the WHO is incorrect.

HAMILTON: Uram also says the proposed ban would not disrupt existing vaccine programs.

URAM: We support an eventual ban. We look at a phase-out. We're not saying that we should just flip a switch.

HAMILTON: The United Nations Environment Program expects to make a decision about the ban next year.

Jon Hamilton, NPR News.

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