AS A PEDIATRICIAN, vaccine researcher and the father of an autistic child, I have great concerns regarding the debate about the safety of our infant and childhood vaccines.  The unfounded association that has been proposed by some between vaccines and autism is at best misleading and at worst a serious  undermining of children's health.
 
     The vaccine/autism question stems from two separate theories that are unscientific and have been determined to be invalid by the qualified experts in vaccine science.  The first claims autism is the result of the combination measles, mumps, rubella (MMR) vaccine. The second claims thimerosal is the autism culprit. Thimerosal is a mercury-based compound that was used in many vaccines since the 1930s, but MMR vaccine does not, and has never, contained thimerosal.
 
 Let's begin with the MMR question.  Numerous large-scale studies have shown no increase in autism for children who received the MMR vaccine. The most recent study, published in The New England Journal of Medicine and funded by the National Alliance for Autism Research, examined more than 500,000 Danish children. The study found there was no greater incidence of autism among children who received the MMR  vaccine than those who did not.
 
  Scientific organizations including the Centers for Disease Control, the Institute of Medicine and the American Academy of Pediatrics have all said that the scientific evidence does not support a causal link between MMR and autism. Ironically, the only known cause of autism is rubella, which the MMR vaccine prevents.
 
   The second vaccine/autism theory is based on the idea that autism is the result of mercury poisoning from the thimerosal in vaccines. In 1999, public health officials decided that thimerosal should be removed from vaccines as a precautionary measure.
 
   A study on thimerosal conducted by the University of Rochester was published last fall in the British medical journal The Lancet. The study showed that ethyl mercury - which is what thimerosal becomes as it is metabolized - is excreted from the body within seven days and does not appear to build up from one vaccination to the next.  Even when it is still in the body following immunization, the levels of this mercury do not exceed the government standard, which is based on a more potentially harmful form of mercury known as methyl mercury - the type found in some types of fish. When the report was released, researchers wrote that children would likely be exposed to more mercury by eating a tuna fish sandwich than by vaccines.
 
   More research into thimerosal is under way, though if thimerosal were the cause of what some believe is a dramatic increase in the incidence of autism, one would expect the incidence to drop dramatically since the removal of thimerosal from vaccines in 1999. But it hasn't.  As the father of a child with autism, I know the need for parents to understand the root of this heartbreaking disorder and find something to blame. However, as a medical doctor, I believe a more constructive focus is on advancing treatment options, extending reimbursement policies and finding a cure.
 
   By focusing on unproved theories, we not only risk wasting our  precious resources and not finding the real cause of autism, but we also risk parents losing confidence in vaccines, resulting in fewer children being immunized. This would leave our youngest vulnerable to diseases that we have only read about in history books, reversing one of the world's most successful public health programs.
 
   A proposed link between autism and vaccines is a distraction that focuses attention away from the real needs of parents of autistic children, namely finding respite care, searching for a child psychiatrist who accepts health insurance, and getting quality special education through public school systems. Ireland and parts of the United Kingdom are a case study of what happens when the fear spreads through the media; fears of the "MMR jab" have led to a significant drop in the immunization rate, resulting in a dramatic increase in the number of measles and mumps cases. We often forget that measles is still the single leading killer of children in the world.   With today's ease of travel, these diseases can quickly be  imported into the United States, putting children who are unprotected at great risk of contracting the disease.

     Every parent has to decide: Is it worth protecting my child from a real, deadly threat or protecting him from a hypothetical, scientifically unproven leap of logic? I chose the former, and I am confident I made the right decision.
 
     PETER HOTEZ is chairman of the Department of Microbiology and Tropical Medicine at George Washington University. He also is a senior fellow and chairman of the Sabin Vaccine Institute's Scientific Advisory Council.   KNIGHT RIDDER/TRIBUNE

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