In preparation for the Committee on Government Reform's June 19 hearing, "The Status of Research into Vaccine Safety and Autism," I am writing to introduce you to the National Network for Immunization Information (NNii) and guide you toward scientifically-credible resources that physicians and nurses look to for guidance on these important issues and can be trusted for their accuracy and reliability. NNii is co-chaired by Dr. Louis W. Sullivan, former U.S. Secretary of Health and Human Services and current president of Morehouse School of Medicine; and Dr. Samuel Katz, professor emeritus of pediatrics at Duke University Medical Center. NNii is funded entirely by private foundations and accepts no support from government agencies or vaccine manufacturers.
NNii, a partnership of medical and nursing professional organizations** was created in 1999 by infectious disease experts, pediatricians, nurses and other health professionals committed to promoting better understanding of-and restoring the declining public confidence in-immunizations. Since its establishment, NNii has become a leading independent, scientifically sound, organization devoted to addressing questions about the effectiveness, value, and safety of vaccines and immunization policies and practices.
Recent NNii research that has guided our efforts in developing information resources and education materials has demonstrated that while the majority of parents support current immunization policies, their understanding of immunizations and the diseases they prevent is limited. Of great concern to us is that a significant percentage of parents have serious misconceptions that may adversely affect their decisions about immunization. For example, NNii's research, "Do Parents Understand Immunizations?: A National Telephone Survey," which was published in the peer-reviewed journal Pediatrics in November 2000, revealed that in this nationally-representative sample of parents of children < 6 years of age, 25% mistakenly feared that their child's immune system could be weakened by too many immunizations. In addition, 19% of parents were not aware that vaccines are evaluated for safety before they are licensed and recommended.
We worry that when "informed" medical decision-making is misinformed, the results can be dangerous. Furthermore, because immunizations impact the control of vaccine-preventable diseases in the individual and in the community at large, decisions about immunizations made by individuals have implications for the health of the public. These decisions must be made on the basis of the best available scientific evidence.
Some of the current concerns about vaccines are, ironically, a result of their effectiveness and success. Since young parents often are unfamiliar with the severity of vaccine-preventable diseases, they question whether the benefits continue to outweigh risks. Driven by concerns appearing in the media, on the Internet and elsewhere, parents and families increasingly worry that vaccines are causing more harm than good and may be responsible for a long list of chronic diseases including asthma, autism, diabetes, learning disabilities, multiple sclerosis, and sudden infant death syndrome.
While we know that no pharmaceutical product is 100% effective or 100% safe and that there are rare but serious side effects following some vaccines, we also know that there is a large body of scientific and epidemiologic information that guides vaccine policy. Before a vaccine can be used in the United States, it must be shown to be safe and effective. Moreover, because healthy children are typically the recipients of vaccines, safety requirements are especially stringent. Once a vaccine is licensed by the Food and Drug Administration (FDA) and recommendations are made by the Advisory Committee on Immunization Practices (ACIP), additional studies conducted by the Centers for Disease Control and Prevention (CDC) and others continue to monitor its effectiveness and safety to assure that it performs in a way that is consistent with the clinical trial and other data that led to its licensure.
We also recognize the appropriate and important role of government oversight, such as that performed by your Committee, in assuring that our immunization policies and practices provide our communities with protection from vaccine-preventable diseases while balancing the risk that may come with this benefit. To this end, we want you to be sure that you are aware of the most up-to-date and scientifically accurate information about two of the issues that are likely to be the focus of the June 19th hearing.
- The possible link between thimerosal (a mercury-containing preservative in some vaccines) and autism; and,
- The hypothesis that the MMR vaccine (measles, mumps and rubella) is linked to the development of autism.
The possible link between thimerosal (a mercury-containing preservative in some vaccines) and autism.
As stated on CDC's website (http://www.cdc.gov/nip/vacsafe/concerns/thimerosal/default.htm), "Thimerosal is a mercury-containing preservative used in some vaccines and other products since the 1930's. No harmful effects have been reported from thimerosal at doses used in vaccines, except for minor reactions like redness and swelling at the injection site. However, in July 1999, the Public Health Service (PHS) agencies, the American Academy of Pediatrics (AAP), and vaccine manufacturers agreed that thimerosal should be reduced or eliminated in vaccines as a precautionary measure. Today, all routinely recommended pediatric vaccines manufactured for the U.S. market contain no thimerosal or only trace amounts."
Because some have theorized that the development of autism and other neurodevelopmental disorders may have resulted from exposure to mercury from the thimerosal that was contained in some vaccines, this issue has recently been reviewed by the Institute of Medicine's Immunization Safety Review Committee. This Committee was formed at the request of CDC and NIH in response to a number of concerns raised about the safety of and the need for certain immunizations. The 15 Committee members have expertise in pediatrics, internal medicine, immunology, neurology, infectious diseases, epidemiology, biostatistics, public health, risk perception, decision analysis, nursing, genetics, ethics, and health communications. To address concerns about the perception that conflicts of interest would have on the acceptance of their reviews and reports, all committee members are free of financial ties to vaccine manufacturers, previous service on vaccine-advisory committees, or prior expert testimony or publications on issues of vaccine safety.
As stated in the IOM's press release that accompanied the release of this report on October 1, 2001, "The committee's comprehensive assessment of the scientific literature on thimerosal included analyses of published and unpublished studies proposing an association with disorders such as autism, and it found them to be inconclusive. No evidence currently exists that proves a link between thimerosal-containing vaccines and autism, attention deficit-hyperactivity disorder, speech or language delays, or other neurodevelopmental disorders."
The Committee went on to state that while the available scientific data do not establish that these neurodevelopmental disorders are caused by thimerosal, at the same time, they do not establish that these neurodevelopmental disorders are not caused by thimerosal. Therefore, the Committee concluded that the hypothesis that exposure to thimerosal-containing vaccines could be associated with neurodevelopmental disorders was "biologically plausible."
In coming to this conclusion, the Committee balanced the following factors. On the one hand they note that the hypothesis that thimerosal exposure through the recommended childhood immunization schedule has caused neurodevelopmental disorders is not supported by clinical or experimental evidence because:
a) Low-dose thimerosal exposure in humans has not been demonstrated to be associated with effects on the nervous system.
b) Neurodevelopmental effects have been demonstrated for prenatal but not postnatal exposures to low doses of methylmercury.
c) The toxicological information regarding ethlymercury, particularly at low doses, is limited.
d) Thimerosal exposure from vaccines has not been proven to result in mercury levels associated with toxic responses.
e) Signs and symptoms of mercury poisonings are not identical to autism, ADHD, or speech or language delay.
f) Autism is thought primarily to originate from prenatal injury.
g) There is no evidence that ethylmercury causes any of the pathophysiological changes known to be associated with autism, such as genetic defects, and there are no well-developed pathological markers of ADHA or delay of speech or language that could be compared to effects of ethlymercury on the nervous system.
On the other hand, the Committee noted that information related to their conclusion of biological plausibility is indirect because:
a) High-dose thimerosal exposures are associated with neurological damage.
b) An extensive toxicological and epidemiological literature establishes methlymercury, a close chemical relative, as a toxicant to the developing nervous system.
c) Some children who received the maximum number of thimerosal-containing vaccines on the recommended childhood immunization schedule had exposures to ethylmercury that exceeded some estimated limits of exposure based on federal guidelines for methlymercury intake.
d) Some children could be particularly vulnerable or susceptible to mercury exposures due to genetic or other differences.
Since the release of the IOM report last year, research supported by NIH's National Institute of Allergy and Infectious Diseases (NIH) demonstrated that mercury derived from thimerosal in vaccines is eliminated in the stool of infants and that mercury levels in children receiving thimerosal-containing vaccines did not exceed, at any time, the blood levels that correspond to the EPA's guidelines for exposure. In addition, an ongoing study of the pharmacokinetics and tissue distribution of thimerosal, ethyl mercury, and methyl mercury in animals supported by NIH and NIEHS will address whether exposure levels established as safe for methylmercury are also appropriate for exposure limits on thimerosal or ethylmercury.
The hypothesis that the MMR vaccine (measles, mumps and rubella) is linked to the development of autism.
This is a topic that is familiar to your Committee, given past hearings. The IOM's Immunization Safety Review Committee, the American Academy of Pediatrics and the British Medical Research Council have reviewed this hypothesis. Each of these independent reviews of both published and unpublished literature has concluded that while there may often be the perception of a temporal link between the administration of the MMR vaccine and the development of signs and symptoms of autism, a causal relationship has not been established.
More specifically, the IOM Committee noted:
a) A consistent body of epidemiological evidence shows no association at a population level between MMR vaccine and autistic spectrum disorders (ASD).
b) The original case series of children with ASD and bowel symptoms and other available case report are uninformative with respect to causality.
c) There is no relevant animal model linking MMR vaccine and ASD.
d) Biological models linking MMR vaccine and ASD are fragmentary.
Regarding the "fragmentary" nature of this hypothesis, the IOM Committee examined the full range of theories that include immunological mechanisms, the opioid excess hypothesis, theories of autoimmunity, and findings by some investigators of the presence of measles virus in the gut of some affected individuals. The full details of this analysis can be found on pages 27-32 of their report, however, the final paragraph of this section further elaborates their conclusion:
"Thus, with the exception of the results from two [research] groups, there is no evidence to support persistent infection with vaccine-strain measles virus except for individuals with compromised immunity. The extant evidence is internally inconsistent; supporting the need for carefully controlled studies to explore these inconsistencies. In the absence of such studies, the evidence does not demonstrate persistent vaccine-strain measles virus infection in ASD, inflammatory bowel disease, or ASD with bowel inflammation. Furthermore, it is not possible with the available evidence to describe the direction of any relationship among vaccine-strain measles virus infection, autism, and enterocolitis - i.e., is it possible that autism creates greater susceptibility to enterocolitis following a viral insult?"
Vaccines are one of medicine's greatest achievements. Without vaccinations, millions of children and adults would contract serious diseases that are now prevented by vaccines, and many would have long-lasting effects or even die.
Yet, the message that the public is hearing through the media and over the Internet is often the opposite: that the risks of immunization may now outweigh their benefits. Unfortunately, we are concerned that this same message may emerge from the June 19 Committee hearing if these issues are not put in the context of the value that vaccines have had and continue to have for individuals, communities and the health of the public. To paraphrase a comment once made by former Secretary of Defense and Secretary of Energy James Schlesinger, "Everyone is entitled to their own opinion...but no one is entitled to their own facts."
We look forward to the work of your Committee regarding issues of vaccine safety and stand ready to do what we can to help you to learn the facts about the many important topics that you will be discussing.
Bruce G. Gelllin, MD, MPH
National Network for Immunization Information
Associate Professor of Medicine (Preventive Medicine)
Vanderbilt University School of Medicine
Associate Professor of Nursing (Preventive Medicine)
Vanderbilt University School of Nursing
Cc: Dr. Louis Sullivan, Dr. Samuel Katz,
Infectious Diseases Society of America, Pediatric Infectious Diseases Society, American Academy of Pediatrics, American Nurses Association, American Academy of Family Physicians, National Association of Pediatric Nurse Practitioners, American College of Obstetricians and Gynecologists.
Additional information about thimerosal in vaccines, can be found at the following web sites:
Institute of Medicine/National Academy of Sciences
IOM's report on thimerosol in vaccines
IOM Vaccine Safety Committee's public meeting on Thimerosal-Containing Vaccines and Neurodevelopmental Outcomes held on July 16, 2001 in Cambridge, Massachusetts.
Centers for Disease Control and Prevention
Food and Drug Administration
MMR vaccine and Autism:
Institute of Medicine/National Academy of Sciences
IOM's report on MMR and Autism
Centers for Disease Control and Prevention
CDC: Vaccines and Autism Theory website
American Academy of Pediatrics
National Alliance for Autism Research
Medical Research Council (United Kingdom)
No New Evidence Of A Link Between Mmr And Autism
General background information on vaccines and immunization:
National Network for Immunization Information
Institute of Medicine's (IOM) Immunization Safety Review Committee
Centers for Disease Control and Prevention's National Immunization Program
Allied Vaccine Group:
This is a web "portal" that provides access to information provided by the American Academy of Pediatrics, the Children's Vaccine Program at PATH, Parents of Kids with Infectious Diseases (PKIDS), the National Network for Immunization Information, the Immunization Action Coalition, the Vaccine Page, and the Vaccine Education Center at the Children's Hospital of Philadelphia.
John's Hopkins Institute for Vaccine Safety
World Health Organization