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Immunization Controversy: A Review of the Issues

Immunization Controversy: A Review of the Issues

Despite publicized controversy, immunizations remain key in the fight against infectious diseases.

As you know, vaccines play a significant role in prevention of the debilitating and, in some cases, fatal effects of infectious disease. Vaccines also provide important benefits in terms of reducing or avoiding costs associated with illness, both direct and indirect.

While vaccines do carry some risks along with the proven benefits, extensive safety standards and monitoring ensure that vaccines are safe for as many people as possible. But ironically, as the value of widespread immunization is proven by continually falling cases of vaccine-preventable diseases, controversies relating to vaccine safety continue to emerge. When the facts are not known, controversies can impact parents’ faith in the safety of vaccines and threaten the health of their children.




Vaccine-Preventable Diseases: 20th Century Annual Morbidity vs. 2005 Morbidity

Following is a review of some of the major vaccine controversies and resolutions. A strong knowledge of the facts behind these issues will enable you to discuss the issues with parents, helping them to make an informed decision about immunization for their family.

MMR vaccine and autism
Controversy: The MMR vaccine protects children from measles, mumps, and rubella, with the first dose usually given at 12 to 15 months of age, and the second dose at 4 to 6 years of age. In 1998, a study of autistic children raised the question of a connection between MMR vaccine and autism.2 The study was later found to have a number of limitations:

  • the study involved only 12 children, not sufficient to make significant conclusions about a link, and did not use a control group
  • the study proposed a link between the timing of the MMR vaccine and onset of autism symptoms without acknowledging that MMR is given at about the time autism is often diagnosed (12-15 months of age)
  • in several of the study children, symptoms of autism occurred before vaccination
  • suggestions that the vaccine caused bowel problems in the children, which then led to autism were made; but in some of the children, autism was diagnosed before bowel symptoms occurred

Resolution: In 2004, 10 of the 13 study authors retracted the study's interpretation, stating that the data were not sufficient to establish a link between the MMR vaccine and autism. It was acknowledged that the study had created serious implications for public health by challenging confidence in the vaccine.3 Other larger studies have since found no relationship between the vaccine and autism. A UK study of 498 children with autism born between 1979 and 1998 revealed that:

  • the percentage of children with autism who received the MMR vaccine was equal to the percentage of unaffected children
  • the age at diagnosis of autism was the same in vaccinated and unvaccinated children
  • the onset of symptoms of autism did not occur within 2, 4, or 6 months of receiving the MMR vaccine.4

Experts including the AAP and the CDC agree that MMR vaccine is not responsible for recent increases in the number of children with autism. In 2004, a report by the Institute of Medicine concluded that there is no association between autism and MMR vaccine.5,6,7

Thimerosal-containing vaccines
Controversy: The vaccine preservative thimerosal (an ethyl mercury preservative) has been hypothesized to have adverse effects due to excessive mercury exposure for infants. The original controversy arose in 1999 with the addition of the new vaccines for hepatitis B and H. influenzae type b, theorizing that the increased mercury load was having adverse neurological effects on infants. Thimerosal has been important to resisting bacterial contamination of multi-dose liquid vaccines, but controversies relating to thimerosal include a suggested link with autism, acute lymphoblastic leukemia and neurological abnormalities.8,9

Resolution: Evidence gathered since the original controversy in 1999 supports the safety of thimerosal and clarifies the minor lifetime risk of the low amounts of mercury the infant is exposed to with vaccines. It has also been clarified that the mercury risk relates to methyl rather than ethyl mercury. It is still acknowledged that some infants may be more sensitive to thimerosal, particularly premature or low birth weight infants. The WHO continues to support use of these vaccines in developing countries because the cost-effective multi-dose formulations make it possible to vaccinate as many children as possible, while providing proven effectiveness and safety. In developed countries, mono-dose, thimerosal-free vaccines are now used in almost all vaccines, at least partly in response to public pressure resulting from the theoretical risks.8-12

Multiple vaccines and the immune system
Controversy: Many vaccines given early in life could overwhelm a child’s immune system, suppressing it so it does not function correctly.

Resolution: There is no evidence to support the suggestion that childhood vaccines can "overload" the immune system. According to Adverse Events Associated with Childhood Vaccines , a 1994 report from the Institute of Medicine, "In the face of these normal events, it seems unlikely that the number of separate antigens contained in childhood vaccines … would represent an appreciable added burden on the immune system that would be immunosuppressive."13 Vaccines given in the first two years of life have been described as "a raindrop in the ocean of what the infant's immune system successfully encounters in their environment every day."14

Resolving immunization controversies through research and education
In response to the numerous issues in recent years regarding vaccine safety, the Global Advisory Committee on Vaccine Safety convened in 2005 to review these issues. They concluded that there are no reliable data to support any of the current controversies, and at the same time emphasized the health risks that can result from a drop in immunizations because of these vaccine “scares”.8

An article published in August 2007 shows that approximately 75% of states in the U.S. report that they have reached the CDC’s Healthy People 2010 objective of having at least 95% of all children entering kindergarten receive their recommended vaccines.15 The global advisory committee emphasized the importance of education to develop an informed and positive attitude with parents regarding childhood immunizations; these recent results seem to show that educational efforts are having an encouraging effect.

References
  1. Orenstein WA. The role of measles elimination in development of a national immunization program. Pediatr Infect Dis J 2006;25(12):1093–101.
  2. Wakefield AJ et al. Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children. Lancet 1998;351(9103):637–41.
  3. Murch SH et al. Retraction of an interpretation. Lancet 2004:363(9411):750.
  4. Taylor B et al. Measles, mumps, and rubella vaccination and bowel problems or developmental regression in children with autism: population study. BMJ 2002;324:393–6.
  5. Kemp, C. AAP panel finds no link between ASD, MMR vaccine. AAP News 2001;18(5):197.
  6. Centers for Disease Control and Prevention.
    http://www.cdc.gov/od/science/iso/concerns/mmr_autism.htm
  7. Institute of Medicine Immunization Safety Review Committee.
    http://www.vaccinesafety.edu/IOMreport-VaxAutism2004.htm
  8. François G et al. Vaccine safety controversies and the future of vaccination programs. Pediatr Infect Dis J 2005;24(11):953–61.
  9. Bigham M, Copes R. Thiomersal in vaccines: balancing the risk of adverse effects with the risk of vaccine-preventable disease. Drug Saf 2005;28(2):89–101.
  10. Clements CJ. The evidence for the safety of thiomersal in newborn and infant vaccines. Vaccine 2004;22(15-16):1854–61.
  11. Clements CJ, McIntyre PB. When science is not enough – a risk/benefit profile of thiomersal-containing vaccines. Expert Opin Drug Saf 2006;5(1):17–29.
  12. Ball LK, Ball R, Pratt RD. An assessment of thimerosal use in childhood vaccines. Pediatrics 2001;107(5):1147–54.
  13. Stratton KR et al. Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Casuality. Vaccine Safety Committee, Institute of Medicine, 1994.
  14. Tucker ME. MMR Vaccine on Trial at Congressional Hearing. Family Practice News, May 15, 2000.
  15. Nation′s Childhood Immunization Rates Remain at or above record levels. August 30, 2007. Centers for Disease Control and Prevention. http://www.cdc.gov