But despite the proven effectiveness of immunizations, questioning the usefulness and safety of vaccines has become a troubling trend.3 To maintain herd immunity and prevent disease outbreaks, an immunization rate of 95% is required. Herd immunity is imperative because not everyone can be vaccinated and some of those who do get vaccinated will not achieve an adequate immune response.4 Due to the decrease in immunizations and a subsequent decrease in herd immunity, measles outbreaks have been reported recently in Texas and New York; 189 cases of measles were reported in 2013, compared with the record low of 34 cases in 2004.5,6
Pertussis, another highly communicable disease, soared to more than 48,000 cases in 2012 in the United States, and 18 deaths were reported, mainly in children under age 3 months.7 In 2013, the incidence of pertussis fell to 24,231 reported cases, due in large part to a decrease in infant pertussis from widespread immunization of adults and adolescents.8 These statistics underscore the need for a robust immunization program. PAs need to be vocal advocates for vaccines to ensure adequate levels of herd immunity and for the benefit of individual patients.
HISTORY OF THE ANTIVACCINE MOVEMENT
To be effective patient advocates, PAs must understand the concerns and misconceptions parents have about vaccine safety and be able to articulate the benefits of vaccines to the ever-increasing antivaccine movement. Although the antivaccine movement seems to be a modern invention, it has existed since the dawn of the smallpox vaccination in the 1700s. The rationale for the criticism of vaccines back then is the same as today—fears about vaccine safety, religious objections, and skepticism of the science. Even Benjamin Franklin withheld the smallpox vaccine from his young son, a decision he came to regret in 1736 when his son died at age 4 from smallpox.9,10 Today's antivaccine movement was shaped by two events. The first was a 1982 film called DPT [sic]: Vaccine Roulette that claimed a link between the DTP (diphtheria, tetanus, pertussis) vaccine and neurodevelopmental disorders. The second was a 1998 paper by Andrew Wakefield published in the Lancet that purported a link between autism and the MMR (measles, mumps, rubella) vaccine; the article was later retracted.11,12 Numerous studies have refuted any link between vaccines and autism or neurodevelopmental disorders. However, these concerns persist among caregivers.13
MYTH: DTP VACCINES CAUSE ENCEPHALITIS
One of the biggest fears of parents is that immunizations cause autism or neurodevelopmental disorders.14 Much of the fear is generated by the ever-increasing numbers of children diagnosed with autism spectrum disorders (ASDs). Another worry is that vaccines lead to chronic diseases such as multiple sclerosis and cancer.15 Different theories are put forth as the mechanism by which vaccines cause harm. As mentioned above the first theory was that the DTP vaccine caused irreversible neurodevelopmental disorders. The DTP vaccine that was believed to cause this adverse reaction was the whole-cell pertussis vaccine that is no longer used in the United States. In 1991, an acellular pertussis vaccine (DTap) was introduced and remains in use. The whole-cell pertussis vaccine was associated with more severe local reactions and an increased risk for convulsions, mainly due to fevers. The risk of encephalitis postvaccine was 1 to 10 cases per 1 million. In the wake of debate as to whether the vaccine caused permanent neurological deficits, the vaccine was changed. Recent studies on the acellular vaccine show no evidence of encephalopathy postvaccine and a much lower incidence of febrile seizures than the whole-cell version.16
MYTH: MMR VACCINES CAUSE AUTISM
Concerns about the DTP vaccine were followed by a new focus on the MMR vaccine and ASDs. This was largely due to the Wakefield paper, which hypothesized that the MMR vaccine caused a reaction in the gut (ileo-cecal lymphoid nodular hyperplasia), that led to a release of brain-damaging peptides that increased ASD risk.11 Wakefield and his team looked at only 12 children. The report was a case series not a rigorous study that involved a control group. The researchers weren't blinded when they reviewed the neuropsychological assessments or the endoscopic findings. Furthermore, the peptide was never identified and the gastrointestinal findings did not predate ASD in some of the children. Even Wakefield stated in the paper that his study did not prove the MMR vaccine was the culprit in ASD, but that it was a theory that needed further review.17 Twenty studies have explored and subsequently refuted the theory that the MMR vaccine was a cause of ASD. The most salient reports were:
* A large Danish cohort study looked at over a half a million children and found no link between the MMR vaccine and ASD. The study reviewed records from three databases in the country that tracked children born from 1991 to 1998. The study was an ideal cohort of subjects and controls because it was able to track 100% of the subjects enrolled. The MMR vaccine was given only by general practitioners who documented vaccinations on a national registry for reimbursement. Diagnosis of ASD was only done by specialists in child psychiatry, and these diagnoses also were tracked by the national registry.18 The study concluded that vaccinated children were at no increased risk of ASD compared with unvaccinated children.19
* Researchers in Canada looked at pervasive developmental disorder rates with respect to MMR vaccination. They found ASD rates increased with a decrease in the MMR vaccination rate, disproving the claim that the MMR vaccine was the cause of ASD.20
After these and many other studies refuted Wakefield's claims, 10 of his 13 coauthors on the study retracted their support for the MMR-autism hypothesis. In 2010, the Lancet retracted the Wakefield study.21 The British Medical Council stripped Wakefield of his medical license in 2010, citing ethical lapses. Wakefield has continued to purport a link between MMR and ASD.22
MYTH: THIMEROSAL IS TOXIC TO THE CENTRAL NERVOUS SYSTEM
Since the 1940s, thimerosal had been used as a preservative to inhibit bacterial and fungal growth in multivial vaccine preparations. Thimerosal was never a part of live virus immunization such as the MMR vaccine.23 In 2001, thimerosal was removed from almost all vaccines due to the increasing concern in the media about potential mercury toxicity from multiple immunizations given to children in the first 6 months of life.24 This concern turned out to be unwarranted for a few reasons: Thimerosal breaks down into ethylmercury, not the more toxic methylmercury found in fish. The two forms of mercury are related but have notable differences. Methylmercury is much more toxic, has a longer half-life, is far more lipophilic, and is excreted much more slowly from the body than ethylmercury. Because of ethylmercury's shorter half-life and rapid metabolism, it does not accumulate in the body and does not cause disease or ASD.25 Researchers also evaluated prenatal exposure to mercury from immunizations and immunoglobulins as well as exposure in early life to thimerosal-containing vaccines. The study examined children from birth to 20 months for autism, ASD, and ASD with regression. No increased risk was seen for any of the three outcomes.26 Eight additional cohort and ecological studies have confirmed that thimerosal does not cause ASD.27 The continued rise in ASD since the removal of thimerosal dispels the myth that thimerosal is to blame.28
MYTH: MULTIPLE VACCINATIONS OVERWHELM THE IMMUNE SYSTEM
When research failed to support a link between MMR or thimerosal and the increasing rates of ASD, attention turned to the quantity of vaccines that children receive in the first year of life. A hypothesis was put forth that too many vaccines overwhelm the immune system and thus cause not only ASD but also diseases such as multiple sclerosis and cancer.29 This hypothesis is incorrect. The infant's immune system from birth is capable of responding to a multitude of immunologic components from viruses or bacteria on a daily basis, via a T cell and B cell response. The goal of most vaccines is to stimulate a response from the B cells that make and secrete antibodies. Vaccines contain the same antigens or immunologic components as a natural or wild infection, but in a weakened form. The immune response is similar, but because the microbe in the vaccine is weakened, it will not be able to replicate and cause disease. The vaccine primes the immune system to protect itself from the more virulent wild form of the disease.30
Each vaccine contains a set amount of antigens or immune components to which the body responds. Although children receive 14 vaccines in the first year of life, due to vaccine technology, they are exposed to a total of 160 immunologic components. To put this in perspective, one bacterium that an infant contracts from the environment can contain up to 6,000 immunologic components.10 Therefore, the immune challenge from vaccines is significantly lower than from naturally occurring microbes, making it highly unlikely that the immune system can be overwhelmed or weakened by the vaccines. Infants can theoretically respond to 10,000 vaccines at one time.31 To confirm this, recent research examined if increasing exposure to antibody-stimulating proteins and polysaccharides in vaccines increased the risk of ASD. The researchers analyzed 256 children with ASD and 752 matched controls from birth to age 2 years. They found no association between the amount of antibody-stimulating proteins or polysaccharides in vaccines, either as cumulative exposure or as a maximum exposure in a single day, and the risk for ASD.32
MYTH: ADJUVANT INGREDIENTS IN VACCINES ARE UNSAFE
The final issue is the role of adjuvants and other agents in vaccines and their link to ASD and other illnesses. The two substances in vaccines that cause concern are aluminum and formaldehyde. The only licensed adjuvant for use in the United States is aluminum, which is used in nonlive vaccines to induce a better immune response. Aluminum is naturally found in the environment in food and water. For example, breastfed babies ingest up to 10 mg of aluminum in the first 6 months of life.33 A formula-fed child ingests up to 120 mg of aluminum in the same time period.33 Vaccines over the first year of life add only an additional 4.225 mg of aluminum.34 Studies confirm that the addition of such a small amount does not harm the body.34 Furthermore, aluminum is excreted by the kidneys in a fairly rapid manner; unless the patient has severe underlying kidney disease, aluminum is unlikely to build up in significant enough amounts to cause disease.35
Formaldehyde is used in vaccines to inactivate viruses (such as polio and hepatitis A) and toxins (such as diphtheria and tetanus). Only a trace amount of formaldehyde is left after vaccine processing. Formaldehyde is a normal component of protein synthesis; a 2-month-old baby weighing 5 kg has about 1 mg of formaldehyde in the blood. A vaccine contains 0.1 mg of formaldehyde and is removed from the injection site in 30 minutes via metabolism in the muscle. Such a small amount does not cause disease.36 The only evidence of cancer from formaldehyde is from long-term exposure to large quantities.37
VACCINE SURVEILLANCE MECHANISMS
Vaccines, like any medical intervention or medication, carry some risk. However, the benefits of vaccines on the whole outweigh the risk. For example, measles-induced encephalitis occurs in 1 child for every 1,000 cases of the disease. Encephalitis from a severe reaction due to the measles vaccine occurs in 1 child for every 1 million doses.38 See Table 1 for documented adverse reactions to vaccines. Three main surveillance systems have been set up to monitor vaccine reactions:
* Vaccine Adverse Events Reporting System (VAERS) is a passive system that anyone (medical provider, patient, or lawyer) can use to report a suspected adverse event, so the system cannot be used to establish causality.39 The benefit of the VAERS system is that it can raise an alarm as to possible unexpected reactions, such as intussusception caused by the original rotavirus vaccine. Intussusception was not seen in the preclinical trial because the number of the trial participants was too small to pick up this rare event. Only when the rotavirus vaccine was given to a very large population of children did the risk of intussusception become evident. This problem was then evaluated through the other two vaccine monitoring systems.
* Vaccine Safety Data (VSD) Link is a system of multiple HMOs used to track patients in the United States. With this system, potential problems can be evaluated via a cohort study with the added ability to look at a control group.10
* Clinical Immunization Safety Assessment (CISA) network is a partnership between the CDC and medical research centers that look at adverse events that might be related to vaccines. When the concern regarding intussusception was found to be accurate, the original rotavirus vaccine was withdrawn from the market.40
With these systems in place, parents and providers can be reassured that vaccines are continually monitored for their safety.
Overwhelming evidence supports the safety and effectiveness of vaccines, and that they do not cause ASD or contain harmful substances. Medical providers need to confront the myths and misconceptions surrounding vaccines so that patients and parents understand the need for immunizations. If the rates of vaccination continue to fall, diseases once thought controlled will increase and once again cause great harm.
3. Ragan P, Duffy DM. Vaccines in childhood: strategies to address concerns of parents. JAAPA
4. DiPaola F, Michael A, Mandel ED. A casualty of the immunization wars: the reemergence of measles. JAAPA
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10. Offit PA, Moser CA. Vaccine Safety and Your Child—Separating Fact from Fiction
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11. Wakefield AJ, Murch SH, Anthony A, et al. Retraction—Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children [retracted 2010]. Lancet
13. Offit PA, Moser CA. The problem with Dr. Bob's alternative vaccine schedule. Pediatrics
14. Dempsey AF, Schaffer S, Singer D, et al. Alternative vaccination schedule preferences among parents of young children. Pediatrics
15. Chatterjee A, O'Keefe C. Current controversies in the USA regarding vaccine safety. Exp Rev Vaccines
16. Pertussis vaccination: use of acellular pertussis vaccine among infants and young children. Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep
. 1997;46(RR-7):1–25. http://cdc.gov/mmwr/preview/mmwrhtml/00048610.htm
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17. Gerber JS, Offit PA. Vaccines and autism: a tale of shifting hypotheses. Clin Infect Dis
18. Tanne J. MMR vaccine is not linked with autism, says Danish study. BMJ
19. Madsen KM, Hviid A, Vestergaard M, et al. A population-based study of measles, mumps, and rubella vaccination and autism. N Engl J Med
20. Fombonne E, Zakarian R, Bennett A, et al. Pervasive developmental disorders in Montreal, Quebec, Canada: prevalence and links with immunizations. Pediatrics
21. Allen GM, Ivers N. The autism-vaccine story: fiction and deception. Can Fam Physician
25. Hurley AM, Tadrous M, Miller ES. Thimerosal-containing vaccines and autism: a review of recent epidemiologic studies. J Pediatr Pharmacol Ther
26. Price CS, Thompson WW, Goodson B, et al. Prenatal and infant exposure to thimerosal from vaccines and immunoglobulins and risk of autism. Pediatrics
27. Schultz ST. Does thimerosal or other mercury exposure increase the risk for autism? A review of the current literature. Acta Neurobiol Exp
31. Offit PA, Quarles J, Gerber MA, et al. Addressing parents' concerns: do multiple vaccines overwhelm or weaken the infant's immune system. Pediatrics
32. DeStefano F, Price CS, Weintraub ES. Increasing exposure to antibody-stimulating proteins and polysacharrides in vaccines is not associated with risk of autism. J Pediatrics
35. Offit PA, Jew RK. Addressing parents' concerns: do vaccines contain harmful preservatives, adjuvants, additives, or residuals. Pediatrics
. 2003;112(6 Pt 1):1394–1397.
38. Atkinson W, Wolfe S, eds. Epidemiology and Prevention of Vaccine-Preventable Diseases
. 12th ed. Washington DC: CDC Public Health Foundation; 2012:173–191.
39. Chatterjee A. Vaccine safety: genuine concern or a legacy of unfounded skepticism. Expert Rev Vaccines
Keywords:© 2014 American Academy of Physician Assistants.
vaccines; thimerosal; autism spectrum disorders; MMR; communicable disease; DTP