Assessing the Risks and Benefits of Thimerosal In Vaccines

A family physician's pediatric ethical challenges are examined.

By Robert H. Brandon, II, BS, CPH

For centuries, societal debate has questioned the appropriateness of vaccination programs as an effectively risk free strategy in preventing infectious diseases. With political dissent and religious opposition in 1721, variolation efforts against the smallpox epidemic were condemned in Boston, but accepted decades later as a safer course of action, even by Benjamin Franklin (Franklin, 1791). In 1790, Edward Jenner’s vaccination theory led to an 1867 British law mandating smallpox immunization, later opposed on political grounds regarding possible adverse effects in 1867 (Feudtner, 2001).

Decades later, the US Supreme Court addressed the question of compulsory vaccination in 1905, noted in the case of Jacobsen v. Massachusetts (US Supreme Court, 1905). However, recent debate still lingers about immunization adverse outcomes, disease status, and vaccination efficacy.

Communities, health professionals, policy-makers, and public health officials share concern about a possible link between thimerosal containing vaccines with autism, attention deficit hypersensitivity disorder, and speech or language delay (IOM, 2004).

Considering the Problem
Current estimates reveal that immunization rates have reached all time highs for 19-35 month-old children (CDC, 2004). Federal safeguarding of vaccination incentive programs, licensed day care regulations, mandatory immunization schedules, and school entry requirements leaves us to question autonomy, informed consent, and liberty while making decisions (Ornstein, 1999). Justice ensues when considering the duty that our society entrusts in both parents and physicians to promote health and immunization compliance.

Currently, 48 states allow parents to refuse vaccinations on religious grounds, 15 states have philosophical exemptions, and all states recognize exemptions when medical contraindications are implicated (Ornstein, 1999).

Philosophical and religious exemptions allow parents to opt their children out of vaccinations when assessing a theoretical risk-benefit scenario; the benefits of vaccination are well documented and proven where as the risks are speculative (Feudtner, 2001).

Is there a fair burden sharing of risks associated with disease, immunization adverse events, or costs of disease care and immunization programs? Should any child be allowed to take advantage of the benefits provided by “herd immunity” against diseases and potentially put collective members of a community at risk for disease? Will free riders erode the commitment to immunization and lower the protective coverage offered by vaccinations?

Immunization programs should address all potential risks and adverse effects with certainty, consequence, and justify the limitation on freedom for populations not exempt from mandatory vaccination schedules from an ethical standpoint.

Specifying the Problem
Because mercury at high doses is known to pose risks, public health programs have addressed recent concerns that thimerosal in vaccines puts children at increased risk for autism (McCormick, 2001). Thimerosal was removed from vaccines in support of the public health goal of reducing mercury exposure in children, infants, and pregnant women by the American Academy of Pediatrics (AAP) and US Public Health Service (USPHS) in 1999 (CDC, 1999).

Thimerosal is an organic mercury compound used as a preservative in vaccines to prevent bacterial and fungal contamination, required by the Food
and Drug Administration before 1999 (IOM, 2004).

However, ethylmercury, from thimerosal in vaccines, has not been studied extensively and its amount in vaccines is small. Methylmercury, from human consumption of seafood, has proven neurotoxicity in animal models and in vitro studies of biological and pathophysiological processes (IOM, 2004).

The additive effects of both forms of mercury are unknown, but are of concern because many children have mercury levels exceeding federally recommended guidelines at birth (Shete, 2002).

Thimerosal was licensed, marketed, and used in over 30 US vaccines until 1999 (IOM, 2004). Today, none of the vaccines used to protect preschool children against infectious diseases contain thimerosal as a preservative, except some influenza vaccines (Fluzone6/Aventis Pasteur, Inc.; Fluvirin/Evans) (FDA, 2004).

Certain meningococcal (Menomune A, C, AC and A/C/Y/W-135/Aventis Pasteur, Inc.) and tetanus-diphtheria vaccines (Td) given to children age seven and older contain thimerosal as a preservative (FDA, 2004).

In recent years, the uses of mercury containing vaccines have declined with newer alternative formulations with no preservatives (Recombivax-HB/Merck). Other vaccines have trace amounts of thimerosal, namely DTaP (Tripedia2 /Aventis Pasteur, Inc.), DTaP-HepB-IPV (Pediarix/ GlaxoSmithKline) and Hepatitis B (Engerix B/GlaxoSmithKline) (FDA, 2004). Further, thimerosal has been used in anti-venins, immune globulin preparations, ophthalmic and nasal products, and skin test antigens (FDA, 2004).

Assessing the Problem
In October 2001, the Institute of Medicine’s Immunization Safety Review Committee concluded that the evidence was proven to be inadequate to either accept or reject a causal relationship between thimerosal exposure in vaccines and neurodevelopmental disorders such as autism, attention deficit hyperactivity disorder, and speech or language delay (IOM, 2004; McCormick, 2001).

Epidemiological studies have not clearly established developmental, immune, metabolic, molecular, or physiological mechanisms that are casually related to the development of autism (IOM, 2004; McCormick, 2001). However, much debate exists about genetic susceptibility theories focusing on possible genetic markers that predispose individuals to abnormal immune reactions and mercury metabolism.

This remains purely speculative as an attempt to explain findings of no association between vaccination and autism in certain subgroups (IOM, 2004). Further, this theory offers no direct evidence to distinguish between possible abnormalities that are strictly antecedents, comorbid disease expressions, or simply causal factors (IOM, 2004).

Autism’s uncertain patterns of etiology, incidence, and prevalence shows no evidence that the immune system plays a direct role in autism, demonstrating a circumstantial link rather than causal with thimerosal in vaccines (IOM, 2004).

Even if a theoretical concern, removing thimerosal from vaccines is needed to maintain the public’s trust regarding the appropriateness of a universal immunization strategy (Shete, 2002). However, the removal of thimerosal from other vaccines on the US market is a more complicated process. Over time, thimerosal free vaccines will increase as manufacturing protocols and resources are expanded (FDA, 2003).

Overall, the benefits of immunizing children at risk for infectious and vaccine-preventable diseases outweigh theoretical risks of thimerosal exposure and subsequent toxicity (Shete, 2002). Paradigms to initiate dialogue between the government, public, and scientific communities are needed for better communication about potential risks and benefits of vaccination programs.

Without increasing public awareness and participation, the public is left to question the safety of vaccination, leading to decreased compliance rates and the reemergence of infectious diseases like diphtheria, tetanus, pertussis, or hepatitis associated bacterial meningitis (Halsey, 2001).

Providers should continue addressing patient concerns, stay current with immunization materials and practices, and use vaccines available in accordance with the currently recommended schedules.

Robert H. Brandon, II BS, CPH is a third year medical student at the New York College of Osteopathic Medicine and a student member of the ACOFP Ethics Committee.