Vaccine safety: genuine concern or a legacy of unfounded skepticism?

The impact of vaccination on the world’s health is difficult to exaggerate. The availability of vaccines to prevent many of the Earth’s worst killer diseases in the past century, has led to billions of lives being saved, decades of life-expectancy increase, enhancement of quality of life and the elimination of a huge burden of suffering and disability around the world. Why then would anyone question the value of this wonderful preventative strategy? Yet, in recent years, as vaccine-preventable diseases have disappeared from the public eye, particularly in developed countries, the specter of vaccines as a dangerous intervention has been raised by some people. To some extent, vaccines have become a victim of their own success.

Attempts to vaccinate go back several centuries but the ‘golden age’ of vaccine development did not begin until the 1940s, with the development of cell-culture techniques. Over the following few decades, vaccine development occurred in leaps and bounds, allowing public-health authorities to gain control of age-old scourges, such as smallpox, measles and polio. These early successes, however, have been tempered in recent years by the rising tide of fear that vaccines do more harm than good.

Two major areas of concern have been the potential adverse effects, particularly neurodevelopmental disorders related to thimerosal (approximately 50% of which is ethylmercury), used as a preservative in some vaccines [1], and the reported but subsequently refuted, association between the measles component of the triple measles–mumps–rubella (MMR) vaccine and autism [2]. Soon after these two hypotheses emerged, several crucial epidemiologic investigations were launched by different investigators and agencies, using a variety of study designs, including cohort, case–control and ecologic, in different populations and countries. Except for studies conducted by one pair of authors [3], all others failed to reject the null hypothesis of no association [4]. The studies published by Geier and Geier [3] contain critical design flaws, such as using data from the Vaccine Adverse Event Reporting System (VAERS), a cooperative program for vaccine safety of the US CDC and the US FDA [101]. VAERS is a passive surveillance system to which anyone may report vaccine-related adverse events, without determining causality. On the other hand, other studies that did not show any relationship between thimerosal and adverse neurodevelopmental disorders were statistically sound, well powered to detect even small effects and could adjust for background confounding factors. As for the study linking the MMR vaccine to autism, that too had major methodological flaws; of the 12 children in the study, some were found to have had developmental disorders before they were vaccinated and most were clients of a lawyer who was preparing to sue vaccine manufacturers [102].

In 2004, the Institute of Medicine Immunization Safety Review Committee reviewed all evidence available from biological, molecular and animal model studies and stated that “The committee concludes that the evidence favors the rejection of a causal relationship between thimerosal-containing vaccines and autism” [5]. Proponents of antivaccine legislation often quote a passage from this report that states that “the committee cannot rule out, based on the epidemiological evidence, the possibility that vaccines contribute to autism in some small subset or very unusual circumstances”, conveniently failing to complete the statement that continues, “however, there is currently no evidence to support this hypothesis either” [5].

Two recently published studies have, again, addressed the issue of vaccine safety, particularly as it relates to autism [6] and other neuropschyological outcomes [7]. The study by Schechter and Grether uses an ecologic design and data from the California Department of Developmental Services from January 1995 through to March 2007 [6]. The authors have shown that the prevalence rate of autism continued to climb during this period, despite the fact that thimerosal was discontinued as a preservative in childhood vaccines in 2001 [6]. The study by Thompson et al. examined 42 neuropsychological outcomes (excluding autism-spectrum disorders) in children between 7 and 10 years of age from four health-maintenance organizations that participate in the CDC’s Vaccine Safety Datalink [7]. The authors conclude that their study does not support a causal association between early exposure to mercury from thimerosal-containing vaccines and immunoglobulins, and deficits in neuropsychological functioning at the ages of 7–10 years [7].

Despite the growing body of scientific literature refuting any association between thimerosal in vaccines and neurodevelopmental disorders in children, and the link between the MMR vaccine and autism being debunked after the Lancet retracted the report by Wakefield et al. and ten of its 12 authors disavowed its findings, powerful, well-funded advocacy groups continue to keep the antivaccine movement alive. Conspiracy theories generated by these groups portray respected investigators, vaccine manufacturers and public-health agencies as public enemies [8]. When their efforts at promoting legislation to restrict access to vaccines failed at a federal level, these groups resorted to lobbying state legislators to pass bills that would ban thimerosal-containing vaccines and limit public-health agencies and private providers from providing many vaccines to children. Unfortunately, such efforts have been at least partially successful in a few states. Having gone before the Health and Human Services Committee of my home state to testify against these bills for several years, I have heard some of the most egregious misinformation spread by those who continue to delude the public of the possible harm caused by vaccines. I am proud to say that this bill has not been passed into law in my state. However, charlatans offering false hope to desperate parents and caregivers continue to peddle ‘tests’ to confirm mercury poisoning and alternative, sometimes dangerous, ‘treatments’ for autism, such as chelation therapy, hyperbaric oxygen and testosterone suppression [9].

Since autism was first described in the 1940s, multiple, unfounded theories of causation and corollary ‘treatments’ have been offered [10]. On a personal note, having grown up with a brother who was autistic, I remember the many years of anguish my mother suffered thinking that somehow her ‘neglect’ had led to his condition. Only in the past few years, with the convergence of rapidly advancing genomic technologies, the completion of the Human Genome Project and successful collaborative efforts to obtain DNA samples from autistic patients for study, have the first solid clues regarding the genetic origins of autism begun to emerge [11–13]. Instead of continuing to conduct studies to demonstrate that vaccines do not cause autism or other neuropsychiatric disorders, it is time to refocus our intellectual and monetary resources on further defining the genetic basis of these terrible diseases, develop scientifically proven therapies and provide succor and support to the patients and families who are affected by these disorders. Providers of healthcare to children need to familiarize themselves with current recommendations for the identification, evaluation and management of children with autism-spectrum disorders that have been published by the American Academy of Pediatrics [14,15].

Vaccines are among the greatest achievements of biomedical science and public health [16]. A recent study compares the morbidity and mortality before and after widespread implementation of national vaccine recommendations for 13 vaccine-preventable diseases in the USA [17]. There was a greater than 92% decline in cases and a 99% or greater decline in deaths due to vaccines against diphtheria, mumps, pertussis and tetanus [17]. Endemic transmission of polioviruses, measles and rubella viruses has been eliminated in the USA and smallpox has been eradicated worldwide [17]. Declines of 80% or greater for cases and deaths have been noted for hepatitis A, acute hepatitis B, invasive Haemophilus influenzae type b and varicella [17]. Significant declines in deaths and diseases due to invasive Streptococcus pneumoniae have also occurred [17]. This impressive record of the success of vaccine programs in the past may lead to complacence regarding these killer diseases. A sobering fact is that young children continue to die in Europe as a result of the MMR–autism scare, and unfounded concerns about vaccine safety continue to pose a risk from vaccine-preventable diseases to children in the USA, as exemplified by the recent measles outbreak [18]. The motivations of a minority of individuals who prey upon the fears of poorly informed parents and caregivers for personal financial gain and notoriety must be exposed. Unfounded theories about vaccine safety based on flawed studies must not be allowed to trump well-designed, scientifically and statistically sound research conducted by respected investigators and published in renowned, peer-reviewed journals. For the gains of the last century to continue in the future, vaccine providers in the USA and around the world must continually update their knowledge of the issues surrounding vaccine safety and reassure concerned parents and caregivers that vaccines remain a life-saving intervention and that there is no scientific evidence to implicate them in a causal relationship with autism or other neuropsychiatric disorders.

Financial & competing interests disclosure

Grant/research: Abbott Labs, Bayer, Bristol-Meyer Squibb, GlaxoSmithKline, MedImmune, Merck, Novartis, Sanofi-Pasteur and Viropharma. Speaker’s bureau: Abbott Labs, AstraZeneca, GSK, MedImmune, Merck, Pfizer, Sanofi-Pasteur and Wyeth. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.