AAP: Vaccine Researchers Preach to Pediatrician Choir
AAP: Vaccine Researchers Preach to Pediatrician Choir
By Neil Osterweil, Senior Associate Editor, MedPage Today
Reviewed by Zalman S. Agus, MD; Emeritus Professor at the University of Pennsylvania School of Medicine.
October 11, 2005
MedPage Today Action Points
* Inform patients that according to this report there is no reliable scientific evidence to support a causal link between childhood immunizations and autism, diabetes, asthma or other chronic conditions.
* Caution reluctant parents that failure to have their children immunized with recommended vaccinations can put them at risk for serious or fatal infections, including seemingly harmless diseases such as measles.
* This study was published as an abstract and presented orally at a conference. These data and conclusions should be considered to be preliminary as they have not yet been reviewed and published in a peer-reviewed publication.
Review
WASHINGTON, Oct. 11 - Vaccine-safety researchers picked a friendly crowd to pronounce that there is no scientific evidence linking thimerosal-containing vaccines or the mumps-measles-rubella (MMR) vaccine with autism or autoimmune disorders.
In a plenary session at the American Academy of Pediatrics meeting here, they emphasized the word "scientific." There's plenty of evidence to go around, they noted, but little if any of the evidence linking childhood vaccinations to autism or other conditions stands up to scientific scrutiny.
"Ever since Ed Jenner started smallpox vaccinations [in 1796] there have been public groups trying to link vaccines to morbidity," said Carden Johnston, M.D., of Children's Hospital in Birmingham, Ala., past president of the American Academy of Pediatrics, in an interview.
"But because we give vaccines to healthy children, we have a special obligation to assure they are safe and that they are used in a safe manner," said Walter A. Orenstein, M.D., director of vaccine and policy development at Emory. "Maintaining public credibility means we have to take vaccine safety concerns seriously, evaluate them scientifically, and disseminate our best assessments of the causal role of vaccines in illnesses and syndromes linked to vaccine in time."
During the session, Dr. Orenstein reviewed the evidence -- strong, shaky, and poor -- for links between childhood immunizations and developmental disorders or diseases.
A 2004 survey of physicians in the United States found that 92% of pediatricians and 60% of family physicians had patients whose parents refused at least one recommended vaccine, he noted.
Among the primary concerns expressed by parents and anti-vaccine crusaders are putative links between autism and the presence of thimerosal; autism in association with MMR vaccine; and multiple immunizations in childhood and their alleged link to diabetes, asthma, and heterologous infections.
"Mercury is a known neurotoxin, and in 1999 it was recognized that thimerosal in the immunization schedule, an ethyl-mercury-containing preservative, might exceed some federal safety guidelines although not others," Dr. Orenstein said.
Evidence to support the link between thimerosal and mercury comes in part from ecologic studies, such as one from California showing an apparent correlation between the number of children seeking special educational services for autism and the estimated mercury exposure from vaccines.
But such studies are subject to biases such as changes in diagnostic codes and criteria, and educational services offered, Dr. Orenstein noted.
He also pointed to a study from NIH and Harvard researchers comparing typical features of children with autism and those with mercury poisoning, and found few similarities between the groups in terms of motor function, vision, speech, sensory function, psychiatric issues, or head size.
Moreover, the form of mercury that causes major toxicities is methyl mercury, not the ethyl mercury contained in thimerosal. Ethyl mercury has a shorter half-life and is less frequently associated with neurologic toxicities than methyl mercury, he noted.
Further evidence suggesting the lack of a thimerosal-autism link comes from Scandinavia. When thimerosal was removed from vaccines in Sweden and Denmark, there was no corresponding change in rates of autism reported in those countries.
There is also evidence to show that at least three studies purporting to find a link between thimerosal and autism met none of eight epidemiologic study quality criteria, compared with four other studies finding no causality link, which met between five and seven or eight quality measures, he noted.
As for charges that MMR vaccine may cause autism, "this was started by the report of Andrew Wakefield of 12 cases of autism and bowel disease, eight following shortly after MMR," Dr. Orenstein said. "They did an endoscopy and found ileal lymphonodular hyperplasia in the bowel, a non-specific abnormality. They speculated the measles virus can cause bowel disease, and then there was a leak of toxins that then lead to autism."
There has been no evidence of autism onset clustering around MMR vaccinations, however, and in studies in Denmark where all children are tracked, there was no evidence of a link between MMR vaccination and autism in regard to age at vaccination, time of vaccination, or years of vaccination, Dr. Orenstein said.
He also cited the findings of an Institute of Medicine committee on vaccine safety, which in 2004 concluded that "the evidence favors rejection of a causal relationship between 1) thimerosal-containing vaccines and autism, and 2) MMR vaccine and autism."
Regarding claims that multiple immunizations could overwhelm the infant immune system and lead to autoimmune conditions or opportunistic diseases, the investigator noted that neonates are capable at birth of generating humoral and cellular immune responses. In addition, they are exposed at birth to a rich microbial environment, and their B-cell responses to T-cell independent antigens is limited until about age two.
Today's vaccines are also highly purified and contain many fewer antigenic proteins and polysaccharides than those produced in earlier decades. In 1980, seven recommended vaccines contained about 3,041 total immunogenic proteins, compared with about 125 total immunogenic proteins in 11 currently recommended vaccines.
"There have been enough studies done trying to link autism to vaccines," Dr. Johnston commented. "To find the cause of autism, research funds should be spent on more productive areas."
By Neil Osterweil, Senior Associate Editor, MedPage Today
Reviewed by Zalman S. Agus, MD; Emeritus Professor at the University of Pennsylvania School of Medicine.
October 11, 2005
MedPage Today Action Points
* Inform patients that according to this report there is no reliable scientific evidence to support a causal link between childhood immunizations and autism, diabetes, asthma or other chronic conditions.
* Caution reluctant parents that failure to have their children immunized with recommended vaccinations can put them at risk for serious or fatal infections, including seemingly harmless diseases such as measles.
* This study was published as an abstract and presented orally at a conference. These data and conclusions should be considered to be preliminary as they have not yet been reviewed and published in a peer-reviewed publication.
Review
WASHINGTON, Oct. 11 - Vaccine-safety researchers picked a friendly crowd to pronounce that there is no scientific evidence linking thimerosal-containing vaccines or the mumps-measles-rubella (MMR) vaccine with autism or autoimmune disorders.
In a plenary session at the American Academy of Pediatrics meeting here, they emphasized the word "scientific." There's plenty of evidence to go around, they noted, but little if any of the evidence linking childhood vaccinations to autism or other conditions stands up to scientific scrutiny.
"Ever since Ed Jenner started smallpox vaccinations [in 1796] there have been public groups trying to link vaccines to morbidity," said Carden Johnston, M.D., of Children's Hospital in Birmingham, Ala., past president of the American Academy of Pediatrics, in an interview.
"But because we give vaccines to healthy children, we have a special obligation to assure they are safe and that they are used in a safe manner," said Walter A. Orenstein, M.D., director of vaccine and policy development at Emory. "Maintaining public credibility means we have to take vaccine safety concerns seriously, evaluate them scientifically, and disseminate our best assessments of the causal role of vaccines in illnesses and syndromes linked to vaccine in time."
During the session, Dr. Orenstein reviewed the evidence -- strong, shaky, and poor -- for links between childhood immunizations and developmental disorders or diseases.
A 2004 survey of physicians in the United States found that 92% of pediatricians and 60% of family physicians had patients whose parents refused at least one recommended vaccine, he noted.
Among the primary concerns expressed by parents and anti-vaccine crusaders are putative links between autism and the presence of thimerosal; autism in association with MMR vaccine; and multiple immunizations in childhood and their alleged link to diabetes, asthma, and heterologous infections.
"Mercury is a known neurotoxin, and in 1999 it was recognized that thimerosal in the immunization schedule, an ethyl-mercury-containing preservative, might exceed some federal safety guidelines although not others," Dr. Orenstein said.
Evidence to support the link between thimerosal and mercury comes in part from ecologic studies, such as one from California showing an apparent correlation between the number of children seeking special educational services for autism and the estimated mercury exposure from vaccines.
But such studies are subject to biases such as changes in diagnostic codes and criteria, and educational services offered, Dr. Orenstein noted.
He also pointed to a study from NIH and Harvard researchers comparing typical features of children with autism and those with mercury poisoning, and found few similarities between the groups in terms of motor function, vision, speech, sensory function, psychiatric issues, or head size.
Moreover, the form of mercury that causes major toxicities is methyl mercury, not the ethyl mercury contained in thimerosal. Ethyl mercury has a shorter half-life and is less frequently associated with neurologic toxicities than methyl mercury, he noted.
Further evidence suggesting the lack of a thimerosal-autism link comes from Scandinavia. When thimerosal was removed from vaccines in Sweden and Denmark, there was no corresponding change in rates of autism reported in those countries.
There is also evidence to show that at least three studies purporting to find a link between thimerosal and autism met none of eight epidemiologic study quality criteria, compared with four other studies finding no causality link, which met between five and seven or eight quality measures, he noted.
As for charges that MMR vaccine may cause autism, "this was started by the report of Andrew Wakefield of 12 cases of autism and bowel disease, eight following shortly after MMR," Dr. Orenstein said. "They did an endoscopy and found ileal lymphonodular hyperplasia in the bowel, a non-specific abnormality. They speculated the measles virus can cause bowel disease, and then there was a leak of toxins that then lead to autism."
There has been no evidence of autism onset clustering around MMR vaccinations, however, and in studies in Denmark where all children are tracked, there was no evidence of a link between MMR vaccination and autism in regard to age at vaccination, time of vaccination, or years of vaccination, Dr. Orenstein said.
He also cited the findings of an Institute of Medicine committee on vaccine safety, which in 2004 concluded that "the evidence favors rejection of a causal relationship between 1) thimerosal-containing vaccines and autism, and 2) MMR vaccine and autism."
Regarding claims that multiple immunizations could overwhelm the infant immune system and lead to autoimmune conditions or opportunistic diseases, the investigator noted that neonates are capable at birth of generating humoral and cellular immune responses. In addition, they are exposed at birth to a rich microbial environment, and their B-cell responses to T-cell independent antigens is limited until about age two.
Today's vaccines are also highly purified and contain many fewer antigenic proteins and polysaccharides than those produced in earlier decades. In 1980, seven recommended vaccines contained about 3,041 total immunogenic proteins, compared with about 125 total immunogenic proteins in 11 currently recommended vaccines.
"There have been enough studies done trying to link autism to vaccines," Dr. Johnston commented. "To find the cause of autism, research funds should be spent on more productive areas."
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