ediatrics infectious disease experts, both nationally and locally, judged misleading a recent local news report about alleged childhood vaccine complications. Physician leaders worry about a negative impact on the health of children in the Dallas community.

A controversial series aired in May by WFAA-TV Channel 8 raised frightening questions concerning a potential causal link between a compound previously used in vaccines and neuro-developmental problems. The report focused on the mercury-containing compound thimerosal, previously used as a preservative in vaccines recommended for routine use in children, and an alleged association with neuro-developmental problems, specifically autism.

However, members of the medical staff at Children’s Medical Center of Dallas are urging parents not to be alarmed by the report and to instead consider the facts. The physicians’ overwhelming support for the use of preventive vaccines was demonstrated in a two-page ad in the June 30 Dallas Morning News, which was signed by nearly 300 doctors and backed by other leading health organizations, including the American Academy of Pediatrics.

Vaccines against infectious diseases are among the greatest achievements of medicine and have spared millions of people from the effects of devastating diseases. A small sampling of the effect of routine childhood vaccines include the following:

• Prior to 1985, Haemophilus influenza type b (Hib) caused more than 12,000 cases of meningitis in children and more than 7,000 cases of serious pneumonia each year.
• In one year, 1964 to 1965, 12.5 million cases of rubella (German measles) existed, including cases during pregnancy that resulted in more than 20,000 sick infants. Of these babies, 11,600 were deaf, 3,580 were blind and 1,800 were mentally retarded.
• Before 1963, more than 3 million cases of measles existed, and there were 500 deaths from measles annually.
• In 1952, polio paralyzed more than 21,000 people.

Because vaccines have been so effective, the rate for these “vaccine-preventable diseases” has declined dramatically. But these diseases can return if immunization rates fall too low. Dallas experienced one of the largest measles outbreaks in the country in 1989 to 1990, when local childhood immunization rates dropped. There were more than 3,000 cases, including 10 deaths.

With the disappearance of the infectious diseases, media attention to the rare but real potential for an adverse outcome to the vaccine itself has increased.

“It is understandable that parents are more fearful of the alleged complications of vaccines than of the diseases they prevent, because we have been so successful at preventing these diseases; we do not see the illness and deaths caused by these diseases anymore,” says Dr. Jane Siegel, an infectious disease specialist on the medical staff at Children’s who also attends the Centers for Disease Control Advisory Committee on Immunization Practices meetings as a non-voting liaison member from the Healthcare Infection Control Practices Advisory Committee.

Still, public health officials and infectious disease experts consistently monitor for vaccine complications. The theoretical concern for a negative impact of mercury in the thimerosal preservative has received extensive review. An Institute of Medicine committee of scientific experts who have no conflicts of interests with vaccine manufacturers reviewed all available information. The committee’s report was released in October 2001 (www.nap.edu/catalog/10208.html). The committee concluded “the evidence is inadequate to accept or reject a causal relationship between thimerosal exposures from childhood vaccines and the neuro-developmental disorders of autism, attention-deficit hyperactivity disorder and speech or language delay.”

“A considerable body of evidence exists to indicate that there is no causal relationship between receiving thimerosal-containing vaccines and neuro-developmental disorders. And, additional studies are ongoing,” Dr. Siegel says.

For more information about vaccines, go to the American Academy of Pediatrics Web site at www.aap.org, the Centers for Disease Control and Prevention Web site at www.cdc.gov/nip and the National Network for Immunization Information Web site at www.immunizationinfo.org.

Physicians on the medical staff at Children’s strongly encourage parents to educate themselves about the real facts of the benefits and risks of vaccines. In doing this, parents must seek the best sources of reliable information. Misleading claims that the organic mercury contained within thimerosal causes neurological damage has fanned public fears, Dr. Siegel says.

The specific issues of mercury and its use as a preservative are complex. “It is important to realize that our knowledge of mercury toxicity is based on information pertaining to the form of mercury found in the environment, methyl mercury. We know less about the form of mercury in thimerosal, ethyl mercury,” Dr. Siegel says. “We do know, however, that there is at least one important difference: The mercury in thimerosal is eliminated from the body substantially about seven times faster than the environmental type of mercury, with a half-life of six to eight days compared with 45 days.”

Multiple national organizations are continuing to evaluate and address the issue. The American Academy of Pediatrics has issued several statements, including one in direct response to the Dallas Channel 8 report. The American Academy of Pediatrics stresses that the dangers of mercury should focus on inorganic mercury, which is found in contaminated water or polluted air, not in vaccines or thimerosal. The National Institutes of Health has backed research demonstrating that tests of infants’ blood, taken within eight days of vaccination, do not show levels of mercury above potentially significant exposure limits.

However, after theoretical concerns were raised, decisions were made to remove thimerosal as a preservative from childhood vaccines, and this was accomplished by March 2001. A survey in February 2002 found thimerosal-containing vaccines in less than 2 percent of supplies in providers’ offices. With the current vaccine shortages, it is highly unlikely that vaccines manufactured prior to March 2001 still would be available, Dr. Siegel says.

The benefits of childhood vaccines are unequivocal. Media reports that are confusing to parents should serve as a useful platform for discussion between parents and physicians about the best ways to keep children healthy.

“We encourage parents to discuss their questions about vaccines with their children’s physician,” Dr. Siegel says.