Concerns about a vaccine preservative long thought put to rest are roaring back to life as a United Nations program considers a worldwide ban on the additive.
The U.N. Environment Program is toiling with the idea of putting the kibosh on thimerosal, an organic mercury compound widely used as a preservative in multidose vaccines since the 1930s. More than a decade ago, a public scare that the additive could cause autism led to the eradication of the ingredient from most childhood vaccines in the U.S. and Europe. But a 2004 FDA report quashed the argument, saying there's no link between thimerosal and autism.
Now health officials and experts find themselves again quelling that same fear. Why put forth the effort? Thimerosal plays a vital role in keeping vaccines fresh and ready to use in the developing world, where refrigeration and single-dose vials may not be an option. If the preservative goes, some experts say, disease could resurge in areas where it has been tempered by vaccines.
Opponents of thimerosal aim to reduce exposure to mercury, which can affect brain development. And most experts agree with this concept, NPR reports.
"But when it comes to thimerosal in vaccines, the benefits far outweigh any risks," Dr. Walter Orenstein of the Emory Vaccine Center at Emory University, author of a paper opposing the ban, told NPR. "This is critical. Lives potentially would be lost if we banned thimerosal from vaccines."
The World Health Organization supports evidence of the preservative's safety. In a 2008 report, the Global Advisory Committee on Vaccine Safety noted a study of mercury in premature and low-birth-weight infants in which those who received a birth dose of hepatitis B vaccine containing thimerosal did not exhibit an accumulation of mercury in blood. Based on the data, the committee recommended that WHO not change its stance on thimerosal-containing vaccines; the additive could stay.
The U.N. Environment Program is expected to make a decision on thimerosal sometime after a final meeting on the issue takes place in January. Should the U.N. support a ban, developing countries may find themselves in trouble because, as Heidi Larson of the London School of Hygiene and Tropical Medicine told NPR, no good alternative to thimerosal exists. Single-dose vaccines, which don't contain the preservative, are expensive and difficult to transport. We'll see where the program lands.