Study Disputes Safety Concerns About Thimerosal
Vaccines that contain thimerosal, a mercury-based preservative, do not cause learning problems or developmental delays, according to a study published on Thursday in the New England Journal of Medicine, the Los Angeles Times reports.
For the study, researchers led by William Thompson, an epidemiologist at CDC, analyzed the medical records of 1,047 children ages seven to 10 enrolled in four HMOs who have received vaccines that contain thimerosal. Researchers examined the vaccination records of participants from birth to age seven months to determine total mercury exposure, with prenatal exposure taken into account (Gellene, Los Angeles Times, 9/27).
Researchers administered to participants 42 neurological and psychological examinations, which included tests to determine their I.Q. levels, their ability to recall a list of names and repeat the names backwards, their manual dexterity and whether they stuttered or had tics (Harris, New York Times, 9/27).
Participants with higher levels of mercury exposure scored higher on 12 tests and lower on seven tests than those with lower levels of exposure, an outcome that did not differ from chance, according to the study.
The study found a link between mercury exposure and small changes in measures of attention, speech and motor control that researchers attributed to chance.
In addition, the study found that boys with the higher levels of mercury exposure had twice the risk for tics as those with the lowest levels of exposure (Los Angeles Times, 9/27).
Anne Schuchat -- an official with CDC, which funded the $5.3 million study -- said that "it's important to say this study isn't of autism," but she added that the agency has begun a separate study "that's going to get at that question to provide more information" (Ricks, Long Island Newsday, 9/27).
According to Schuchat, the results of the study are "very reassuring for parents" whose children received vaccines that contain thimerosal, which manufacturers began to eliminate in 1999 (Sataline, Wall Street Journal, 9/27).
"The bulk of the study really found very, very similar performance in children who were exposed to high amounts of thimerosal and children who were exposed to low or no thimerosal," Schuchat said, adding, "So the totality of the results ... continue to reaffirm the safety of vaccines" (Long Island Newsday, 9/27).
In an editorial that accompanied the study, Paul Offit, chief of the Division of Infectious Diseases at Children's Hospital of Philadelphia, wrote that the study provides the "most comprehensive to date" on a potential link between thimerosal and learning problems and indicates "no evidence of neurologic programs in children exposed to mercury-containing vaccines or immune globulins" (Manning, USA Today, 9/27).
Offit wrote, "The aim of scientific research is to find the truth -- and eventually truth emerges. A truth has emerged here. Vaccines do not cause neuropsychological disorders. So let's move on" (Long Island Newsday, 9/27).
According to the New York Times, the study "is unlikely to end the increasingly charged debate about vaccine safety."
Sallie Bernard, executive director of SafeMinds who served on a board that helped to design and oversee the study, said that the results did not support the conclusions of researchers (New York Times, 9/27).
Bernard said that the study results are "inconclusive" and that the "interpretation of the data is too sweeping" (Wall Street Journal, 9/27).
She said, "The way the study was written was biased," adding, "There are some red flags on tics and language and behavioral control that are concerning and suggest a need for further research" (USA Today, 9/27).
An abstract of the study is available online.
NBC's "Nightly News" on Wednesday reported on the study. The segment includes comments from Schuchat and Laura Bono, a spokesperson for the National Autism Association (Bazell, "Nightly News," NBC, 9/26). Video of the segment is available online.