Background

Autism is a brain development disorder that can result in difficulties in verbal and non-verbal communication and social interaction. People with autism may have different ways of learning and interacting. Autism may also cause repetitive behaviors, intellectual disability, as well as problems with motor coordination, concentration, and sleeping. Signs and symptoms usually start when a child is about 2 to 3 years old.

There are 2 million people in the US with autism, about 1 in 68 children and 1 in 42 boys.

Why is there a concern?

There are widespread concerns and controversy regarding the link between vaccines and autism. Thimerosal, a preservative ingredient used to inhibit growth of bacteria and fungi in vaccines, has been pinpointed as a possible culprit. Thimerosal is believed to contain mercury which can be toxic to the brain. Advocacy groups, the media and celebrities have all played a major role in promoting the notion that thimerosal in vaccines causes autism.

This idea is mainly based on studies conducted in the 1990s by Dr. Mark Geier, a geneticist and former researcher. He was a witness in several vaccine injury cases brought before the National Vaccine Injury Compensation Program. After reviewing data from the Vaccine Adverse Event Reporting System (VAERS), he concluded that children exposed to thimerosal in vaccines are 6 times more likely to have autism compared to unexposed children. VAERS is a national program that collects information from patients and healthcare professionals about vaccine side effects.

Why there shouldn’t be a concern

Dr. Geier’s methodology has been widely criticized by many scientists and researchers, citing that VAERS data alone cannot be used to draw such conclusions. This is because the system collects reports of vaccine injuries but cannot verify their legitimacy or whether the injury was directly caused by the vaccine. Geier’s studies are also thought to be flawed because they do not specify how data was generated, preventing an accurate review of study methods and replication of outcomes.

Although exposure to high levels of mercury can be toxic, there is a difference between the mercury that is found in thimerosal and mercury found in water, soil and certain types of fish. The mercury found in the environment (methyl mercury) can accumulate in human tissue and affect brain development in children. However, the mercury found in thimerosal (ethyl mercury) is not likely to accumulate in human tissue. This was based on a research study by the National Institute of Allergy and Infectious Diseases. Blood levels of infants who had been immunized with vaccines containing thimerosal were tested. It was found that large amounts of ethyl mercury were excreted in infants’ stool after exposure.

Nevertheless, in 2001 the removal or reduction of thimerosal in vaccines for children 6 years old or younger was started as a precautionary measure.

Visit the FDA website for a list of thimerosal content of various vaccines.

The IOM (Institute of Medicine), the FDA (Food and Drug Administration), the American Academy of Pediatrics and the CDC (Centers for Disease Control) all agree that there's likely no relationship between autism and vaccines.

An IOM review of 200 epidemiological and scientific studies concluded that vaccines do not cause autism. Another review of medical and scientific evidence on vaccines and their adverse effects found that vaccines are generally safe and that serious adverse events rarely occur.

The CDC reviewed evidence from studies that examined trends in vaccine use and changes in the frequency of autism. It issued a statement in 2007 stating that the evidence does not support an association between vaccine use and autism.

The FDA, which is responsible for regulating vaccines in the US, conducted a review of the use of thimerosal in childhood vaccines. It concluded that there was no evidence of harm caused by thimerosal used as a preservative in vaccines, except for local allergic reactions.

After a study that reviewed records from managed care organizations and interviews with parents of 256 children with Autism, the American Academy of Pediatrics stated that thimerosal does not increase the risk of autism.

Furthermore, research and evidence have shown that the following factors may increase the risk of getting autism:

• Having certain genes that are associated with autism. Also having a sibling with autism may increase the risk of getting it
• If both parents are older at the time of conception
• If the mother is sick during pregnancy. The state of the mother’s immune system during pregnancy may play a role.
• Difficulties before, during, and right after birth, such as those which cause lack of oxygen to the baby’s brain.
• Having chromosomal disorders such as Fragile X syndrome.
• If the mother takes medications such as valproic acid and thalidomide during pregnancy.

What are healthcare organizations doing?

Research efforts are underway to better understand autism and whether there is a possible association with vaccines. For example, the FDA is currently monitoring VAERS reports. It is also conducting a follow-up study of VAERS reports by reviewing medical records and interviewing patients who have reported cases of autism after receiving vaccinations. Furthermore, the FDA is also conducting laboratory studies on neonatal rats to further understand the biological mechanism of autism.

What should patients do?

It is important to weigh the risks of not vaccinating a child versus the benefits.  Vaccinating a child helps protect them from serious diseases and possibly save their life. It also protects other people in the community from getting sick. A reduction in vaccinations could lead to outbreaks of diseases such as measles, bacterial meningitis and pertussis (whooping cough).  

Pertussis is a very contagious disease that is spread when people inhale bacteria when infected people cough or sneeze. It causes violent coughing and trouble breathing. It can also lead to pneumonia (a serious lung infection), spasms, brain damage and death.

There has been a troubling increase in the prevalence of pertussis in babies and young children. In 2012, 48,277 cases of pertussis were reported to the CDC, including 20 that resulted in death. Most of the deaths were babies younger than 3 months old. From January to June of this year, 9,964 cases of pertussis have been reported to the CDC, which is 24% higher than last year.

Patients should educate themselves and be careful to seek information from reputable healthcare organizations. There is vast amount information on different websites regarding this issue, but some may be inaccurate and not based on scientific evidence. Misinformation could reduce vaccination rates, resulting in an increase in preventable diseases and deaths. For example, some opponents of vaccinations claim that thimerosal in the MMR (Measles, Mumps, Rubella) vaccine causes autism. However, according to the FDA, the MMR vaccine never contained thimerosal.

Patients should also consult their healthcare providers and make the best healthcare decisions for themselves and their families.

Conclusion

It is evident that the initial claims linking vaccines to autism cannot be fully substantiated. Based on the available information, it would appear that the risk of not receiving vaccination may be far much worse than the risk of rare side effects from vaccinations.

This controversy is not likely to end soon but further investigations and research should provide more answers.

Additional resources for information about thimerosal and vaccine safety

Centers for Disease Control and Prevention

Food and Drug Administration

American Academy of Pediatrics

Institute of Medicine

References

Adverse Effects of Vaccines: Evidence and Causality. Institute of Medicine. Available at:

Autism spectrum disorder (ASD): Facts about ASD. Centers for Disease Control. 

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Cohen D, et al. Specific genetic disorders and autism: Clinical contribution towards their identification. J Autism Dev Disord. 2005; 35(1): 103-116

Concerns about Autism. Centers for Disease Control. 

Durkin MS, et al. Advanced parental age and the risk of autism spectrum disorder. Am J Epidemiol. 2008; 168(11): 1268-1276

FDA Statement. Ongoing Response to Vaccines and Autism Issues.

Gardener H, et al. Perinatal and neonatal risk factors for autism: a comprehensive meta-analysis. Pediatrics. 2011; 128(2): 344-355

Geier MR, et al. Neurodevelopmental disorders after thimerosal-containing vaccines: a brief communication. Exp. Biol. Med. (Maywood). 2003 June. 228 (6): 660–4

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Huquet G, et al. The genetic landscapes of autism spectrum disorders. Annu Re Genomics Hum Genet. 2013; 14: 191-213

Immunization Safety Review: Vaccines and Autism. Institute Of Medicine. 

Pichichero, M, et al. Mercury Concentrations and Metabolism in Infants Receiving Vaccines Containing Thiomersal: A Descriptive Study. The Lancet 360.9347 (2002): 1737-741.

Rosenberg RE, et al. Characteristics and concordance of autism spectrum disorders among 277 twin pairs. Arch Pediatr Adolesc Med. 2009; 163(10): 907-914

Stromland K, et al. Autism in thalidomide embryopathy: a population study. Dev Med Child Neurol. 1994; 36(4): 351-356

Thimerosal in Vaccines. Institute Of Medicine. 

Timeline: Thimerosal in Vaccines (1999-2010). Centers for Disease Control

Pertussis Outbreak Trends. Centers for Disease Control. 

Pertussis (Whooping Cough). Centers for Disease Control. Available at: http://www.cdc.gov/pertussis/about/complications.html (Updated Jan 15, 2013). Accessed July 28, 2014

Pertussis (Whooping Cough). Centers for Disease Control. 

Price, C. S., et al. "Prenatal and Infant Exposure to Thimerosal From Vaccines and Immunoglobulins and Risk of Autism." Pediatrics 126.4 (2010): 656-64

Vaccines. National Institute of Allergy and Infectious Diseases.

What Is Autism? What is Autism Spectrum Disorder? Autism Speaks