Developing nations rely on vaccines containing thimerosal, Orenstein said. The preservative is used in vials that contain more than one dose of a vaccine, to prevent contamination, which can happen when a syringe needle is inserted into the vial.
Rich countries such as the United States can get around the need for thimerosal by using single-dose vials. But for poor countries, multi-dose vials make vaccination programs more feasible, Orenstein explained.
Switching to single-dose vials would pose practical problems. For instance, local clinics would need much more refrigeration space to house the same number of vaccine doses, Orenstein said.
Offit agreed. "These countries have limited resources," he said. "Children there are already under-vaccinated. If there's a ban, we'll be under-vaccinating them even more."
The AAP and WHO statements are in response to an international treaty being hammered out by the U.N. Environmental Program. The treaty would try to reduce mercury exposure from a variety of sources -- from consumer products to medical equipment to emissions from coal-fired power plants. The UN is considering including thimerosal on that list.
Dr. Michael Smith, a pediatric infectious disease specialist at the University of Louisville in Kentucky, said he agreed with the AAP stance.
"Since 1999, there have been multiple studies that have not found any link between thimerosal and autism, but at the time this information did not exist," Smith said, so the United States decided to be cautious and remove the preservative.
"It turns out this was not necessary," Smith said.
Offit used stronger terms. "We made a mistake in our country," he said. "To make the same mistake now, with the information
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