By Linda Little for Medscape
A vaccine safety expert reiterated once again that there is no scientific proof linking vaccines to autism or other diseases such as diabetes or asthma.
Current scientific research does not implicate thimerosal-containing vaccines or the measles-mumps-rubella (MMR) vaccine with autism, asthma, or infection, according to Walter Orenstein, MD, professor of pediatrics and director of the Emory Vaccine Center at Emory University School of Medicine in Atlanta, Georgia. He spoke to a packed crowd here at a plenary session of the American Academy of Pediatrics National Conference and Exhibition.
Still, many parents are questioning the safety of such vaccines. Dr.
Orenstein cited a 2004 survey of U.S. physicians in which 92% of pediatricians and 60% of family practitioners reported at least one parental refusal of one recommended vaccine.
Parental concerns expressed to physicians included possible links between autism and thimerosal-containing vaccines, autism and the MMR vaccine, and the possible link between the use of multiple vaccinations and diabetes, asthma, and infection.
It is imperative that the medical profession ensure the safety of vaccines, but it is equally important that the science behind studies is examined, Dr. Orenstein said.
One study in his review that raised parental fears of the connection between thimerosol and autism was a California ecological study that showed an apparent connection between children with autism in special education classes with estimated mercury exposure from vaccines.
“This was an ecological study,” Dr. Orenstein commented. “This could have been due to a change in diagnostic codes as well as the number of available educational services for autism. This would be easily studied in a better epidemiological study.”
He also pointed to a National Institutes of Health and Harvard study that compared the features of children with autism and nonautistic children with mercury poisoning. The study found few similarities between the groups in motor function, vision, speed, sensory perception, and psychology.
There are major differences between traditional mercury poisonings and thimerosal, Dr. Orenstein said. “Not all mercuries are the same.”
Methyl mercury implicated in the usual mercury poisoning is quite different from the ethyl mercury contained in thimerosal, he explained.
“Ethyl mercury has a shorter half-life and is less associated with poisoning.”
Dr. Orenstein cited a study conducted in Sweden and Denmark that did not find a link between thimerosal and autism. When thimerosal was removed from the vaccines in Sweden and Denmark, there was no correlating change in the rates of autism reported in either country, he said.
In reviewing other pertinent studies, it was found that three studies showing a link between thirmerosal and autism did not meet any of the eight established epidemiologic study quality criteria, while four studies finding no link met between five and seven of the quality criteria.
In addition, when an Institute of Medicine committee reviewed published and unpublished studies in 2004, the group found no supporting evidence for a causal relationship between thimerosal-containing vaccines or the MMR vaccine and autism.
Current vaccines given during the first six months of life have essentially no mercury, except trace amounts, Dr. Orenstein said. “There is virtually no mercury.”
Vaccines today are much more highly purified than in the past, he said. “They are not being overloaded with antigenic proteins.”
In addition, Dr. Orenstein concluded, “epidemiological evidence shows no relationship between those with multiple immunizations and asthma nor infections.”
“There have been enough studies done trying to link autism to vaccines,” Carden Johnston, MD, past president of the American Academy of Pediatrics of Birmingham, AL, told Medscape. “Ever since Ed Jenner started smallpox vaccinations, there have been public groups trying to link vaccines to morbidity.” Research funds should be spent on more productive areas, he concluded.
AAP 2005 National Conference and Exhibition: Plenary Session.
Presented Oct. 11, 2005.
Reviewed by Gary D. Vogin, MD