Current Controversies in the USA Regarding Vaccine Safety

Archana Chatterjee; Catherine O'Keefe

Disclosures

Expert Rev Vaccines. 2010;9(5):497-502. 

In This Article

Neurodevelopmental Concerns: Disconnecting Autism

One of the most contentious vaccine controversies to date is the proposed causal relationship between the receipt of the measles–mumps–rubella (MMR) vaccine and autism. Andrew Wakefield, a gastroenterologist in the UK, was the first to postulate the so-called 'leaky-gut' theory. Wakefield's theory was supported by studies that identified measles virus nucleic acid sequences in the blood cells and intestinal tissue of some children who had experienced severe behavioral regression.[12,13] A similar investigation with a larger sample failed to reveal persistence of measles virus nucleic acids in the peripheral blood of children with autism-spectrum disorder.[14] Subsequently, results of several large population- and ecologic-based studies have failed to provide any support for Wakefield's theory.[15] In light of the compelling evidence refuting Wakefield's contention, most of his coauthors have published a formal retraction of the findings of the original article and the journal Lancet has recently fully retracted the original publication based on several elements of the paper being proven to be false.[16,17] Further details about this controversy and autism research have been published in a recent book.[18] The Institute of Medicine (IOM) in a report on vaccine safety has stated that "the committee concludes that the evidence favors rejection of a causal relationship between MMR vaccine and autism".[19] Although there are rare side effects such as immediate hypersensitivity reactions and febrile seizures, as well as mild fever and rash that occur relatively commonly in association with its use, the MMR vaccine continues to be safe, efficacious and recommended by the Advisory Committee on Immunization Practices (ACIP) of the US CDC, and endorsed by the American Academy of Pediatrics (AAP) and the American Academy of Family Practice (AAFP).

Thimerosal is another hot button issue that has been debated in relationship to the onset of autism. Thimerosal has served as a preservative in vaccines since the 1930s. It is added to multidose vaccine vials for its bactericidal properties to preserve the sterility of the contents. In the late 1990s, the government became aware of and concerned about mercury exposure in the general population and the Environmental Protection Agency (EPA) published standards of safe limits of methylmercury exposure.[20] Thimerosal contains 49.6% mercury by weight and metabolizes into ethylymercury and thiosalicylate.[15] The use of thimerosal came under fire as more thimerosal-containing vaccines were added to the recommended infant and child immunization schedule. The possibility of subsequent neurodevelopmental problems related to the cumulative amounts of thimerosal that a child was receiving in the first 2 years of life, the total amount of mercury being administered at a single clinic visit, especially for the very smallest of infants (including premature infants in whom safety data were unavailable at the time) were raised as concerns.[20,21]

In 1999, the AAP and the US Public Health Service (USPHS) took a cautionary stance and issued a joint statement calling for the removal of thimerosal from pediatric vaccines.[22] At that time, the risks of low-dose ethylmercury in vaccines were unknown, although there was no evidence that thimerosal-containing vaccines contributed to toxic mercury levels. Studies conducted subsequently suggest that ethylmercury behaves very differently to the more concerning environmental neurotoxin methylmercury.[21] The action taken by the AAP and USPHS had a significant ripple effect on the general public's acceptance of vaccine safety. The birth dose of hepatitis B vaccine, which at the time contained thimerosal, was subsequently withheld by many healthcare providers and the hepatitis B vaccination campaign experienced a serious setback. The removal of thimerosal from vaccine vials has also increased production costs, which are ultimately passed on to the consumer. At present, with the exception of some influenza vaccines, none of the routinely recommended pediatric vaccines contain thimerosal as a preservative.

In spite of overwhelming scientific evidence to the contrary, the debate rages on with media reports fueling the general public's fear and erosion of confidence in vaccines. In March 2008, the story of Hannah Poling, a 9-year-old child whose parents claimed that she developed severe neurodevelopmental problems after receiving the MMR and other vaccines, found its way to front page news. The MMR–autism 'link' and the hypothesis that multiple vaccines cause autism were given 'new life' when the Polings were successful in their litigation under the Vaccine Injury Compensation Program (VICP). The VICP was developed to fairly compensate individuals who feel they have been harmed by a vaccine. Unlike most US legal claims, the VICP only requires a biologically plausible theory and not irrefutable proof.[23]

The following year on 12 February 2009, the US Court of Federal Claims denied damages for three families who were seeking redress for what they believed to be MMR vaccine-associated neurodevelopmental harm to their children. The three cases were considered 'test cases' for the almost 5000 families with pending claims. The hearings were conducted over 2 years and included 5000 pages of expert testimony and 939 medical articles.[102] This was a landmark decision that was criticized by antivaccine activists and lauded by the Department of Health and Human Services (DHHS). Once again, the purported link between MMR, as well as thimerosal, and autism had been disconnected.

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