WEDNESDAY, Jan. 30 (HealthDay News) -- The latest chapter in the debate over whether childhood vaccines can cause autism was written Wednesday with release of a study that showed the controversial mercury-containing preservative thimerosal is rapidly excreted from babies' bodies and can't reach toxic levels.
"Thimerosal has been used for decades, but the surge in vaccinations caused fear that possible accumulations of ethyl mercury, the kind in thimerosal, might exceed safe levels -- at least, when based on the stringent risk guidelines applied to its better-understood chemical cousin, methyl mercury, which is associated with eating fish," lead researcher Dr. Michael Pichichero, a professor of microbiology/immunology, pediatrics and medicine at the University of Rochester, said in a statement.
"One of the unanswered questions when this first popped up as a controversy was, when you got thimerosal as an injection, how long would it stay in your blood," study co-author Dr. John Treanor, a professor of medicine at the University of Rochester Medical Center, said.
The new research, he added, showed that "the levels of thimerosal don't go very high, and they go down right away. By the time it's time for the next dose of vaccine, the levels are right back to where they were at the beginning."
For its study, Pichichero's team tracked 216 infants from R. Gutierrez Children's Hospital in Buenos Aires, Argentina, where thimerosal is still routinely used in vaccines. Use of thimerosal in childhood vaccines was discontinued in the United States after a joint decision in 1999 by U.S. health officials, pediatricians and vaccine manufacturers.
The infants in the study were put into three age groups and their blood-mercury levels were tested both before and after vaccinations were given to newborns, and at their 2- and 6-month checkups.
Pichichero's group found that for all three age groups, the half-life of ethyl mercury in the blood -- the time it takes for the body to get rid of half the mercury, and then another half, and so on -- was 3.7 days. That's significantly less than the half-life of methyl mercury, the kind found in fish, at 44 days.
"Until recently, that longer half-life was assumed to be the rule for both types of mercury. Now it's obvious that ethyl mercury's short half-life prevents toxic build-up from occurring. It's just gone too fast," Pichichero said.
"If you thought thimerosal was responsible for autism, you would be looking at mercury levels that were far below anything anyone's previously thought as being toxic," Treanor added.
"Though it's reassuring to affirm that these immunizations have always been safe, our findings really have greater implications for world health," Pichichero said. "Replacing the thimerosal in vaccines globally would put these vaccines beyond what the world community could afford for its children."
The findings were to be released Monday in the February issue of Pediatrics, but they were released early by the journal's publisher, the American Academy of Pediatrics (AAP), which is requesting that the ABC network cancel the premiere episode of a new show Thursday dealing with the thimerosal-autism controversy.
The findings also follow a recent report from the California Department of Health that rates of autism continue to climb there even after thimerosal has been removed from childhood vaccines.