An Ounce of Prevention: Communicating the Benefits and Risks of
Vaccines to Parents
Myths Regarding Immunization
Jay M. Lieberman, MD
Vaccines are one of the most powerful tools to keep our children
healthy and were recognized by the Centers for Disease Control and Prevention
as one of the 10 greatest public health achievements of the 20th
century.1 However, myths, misconceptions and misperceptions about
vaccines and, in particular, about the safety of vaccines threaten immunization
programs and consequently the health of our children.
Vaccine myths are dangerous because they can lead to the perception
that vaccines are unsafe. Perceptions matter because they influence behavior,
and concerns about safety can erode confidence in vaccines and cause some
parents to refuse to have their children vaccinated. If too many parents refuse
vaccination, this can lead to the reemergence of infectious diseases that have
been virtually eliminated. For example, fears about the safety of whole-cell
pertussis vaccine led to the temporary discontinuation of pertussis
immunization programs in a number of countries.2 Predictably, as
immunization levels fell, these countries experienced dramatic increases in the
incidence of pertussis.
Similarly, concerns about a possible link between the
measles-mumps-rubella (MMR, M-M-R II, Merck & Co.) vaccine and autism have
resulted in decreased MMR immunization levels in the United Kingdom with
resultant increases in measles and mumps cases.
Vaccine knowledge
According to a study that examined parents’ knowledge about
vaccines, 87% of parents deemed immunizations extremely important to keep their
children healthy. In addition, children’s health care providers were cited
as their most important source of information about immunizations.3
Therefore, physicians and nurses can significantly influence the decisions that
parents make about vaccines.
Figure 1. Number of Antigens in Vaccines
(Reprinted with
permission from Pediatrics. 2002;109: 124-129.)
Despite the general recognition that vaccines are beneficial, some
parents had important misperceptions about vaccines. According to the study,
23% of parents thought that children receive more immunizations than are good
for them and 25% thought a child’s immune system could be weakened as a
result of too many immunizations.3 Unfortunately, these myths are
common not only among parents. According to a poll of the physician audience at
the interactive symposium “An Ounce of Prevention: Communicating the
Benefits and Risks of Vaccines to Parents,” 40% of attendees believed that
children receive more immunizations than are good for them and 12% were unsure
if too many immunizations could weaken the immune system.
Because vaccines are preventative and are usually given to healthy
individuals, they must be as safe as possible, and it is important for parents
and physicians to understand vaccine safety issues. This understanding,
however, should be based upon proof not theory, upon science not
anecdote.
Immune dysfunction
The idea that too many immunizations can overload or damage the
immune system is not based on scientific evidence. Theoretically, infants have
the capacity to respond to 10,000 vaccines at one time,4 and
clinical studies have shown that infants and children are capable of generating
protective humoral and cellular immune responses to multiple vaccines
administered simultaneously.
Furthermore, although the immunization schedule has greatly expanded
over recent decades and children receive more vaccines than ever, they are
exposed to fewer antigens.4 In 1960, children received vaccines
against five diseases: smallpox, diphtheria, tetanus, pertussis, and polio. The
smallpox vaccine contained approximately 200 antigens and the whole-cell
pertussis vaccine approximately 3,000 antigens.
With the global eradication of smallpox, the smallpox vaccine was
removed from the immunization schedule. In addition, the whole-cell pertussis
vaccine has been replaced by the acellular pertussis vaccines, which contain
only two to five antigens. Therefore, although vaccines today protect children
against many more diseases, the number of antigens contained in all of the
recommended vaccines has decreased from more than 3,200 to fewer than 130
(Figure 1).
The Institute of Medicine (IOM), part of the National Academy of
Sciences, formed an Immunization Safety Review Committee to evaluate the
evidence on a series of immunization concerns. The committee consists of 15
health professionals who have expertise in areas including pediatrics,
immunology, infectious diseases, neurology, epidemiology, public health, and
risk perception and communication. A key feature of the committee is that
members have no real or perceived conflicts of interest.
One issue that the committee considered was vaccines and potential
immune dysfunction, including autoimmune and allergic diseases.5
Considering the evidence, the committee favored rejection of a causal
relationship between multiple immunizations and an increased risk of
heterologous infections, meaning that vaccination does not increase a
child’s risk of serious infection, such as pneumonia or meningitis, in the
post-vaccine period. In addition, the evidence suggests that vaccines do not
cause Type 1 diabetes as some have alleged. The data were inadequate to accept
or reject a causal relationship between multiple immunizations and an increased
risk of allergic disease, particularly asthma.
Vaccine adverse events
Many myths center on serious adverse events purported to be caused by
vaccines. As with all drugs, vaccines have adverse events, most of which are
local reactions that are mild and self-limited. Rarely, vaccines are associated
with serious adverse events, such as the oral rotavirus vaccine and
intussusception or the oral polio vaccine and paralytic poliomyelitis.
However, there are common misperceptions about vaccine side effects.
Vaccines have been blamed for supposed relationships with a number of chronic
conditions for which the etiologies remain unknown. For example, it has been
alleged that hepatitis B vaccines may cause demyelinating neurologic disorders,
such as multiple sclerosis (MS). The genesis of these allegations was anecdotal
reports of individuals who developed disease after vaccination.
In 2001, two studies published in the New England Journal of
Medicine found no association between hepatitis B vaccination of adults
and the development of MS or relapse of MS.6,7 Analyzing the
evidence, the IOM favored rejection of a causal relationship between the
hepatitis B vaccine administered to adults and the development of MS or MS
relapse, although there was weak evidence for a biological mechanism by which
the hepatitis B vaccine could possibly influence an individual’s risk of a
demyelinating neurologic disease. Data were inadequate to evaluate the
relationship between hepatitis B vaccination and other demyelinating diseases,
such as Guillain-Barré syndrome, acute disseminated encephalomyelitis,
optic neuritis or transverse myelitis.8
MMR and autism
One of the most prevalent myths recently promoted by anti-vaccine
groups has been that the MMR vaccine causes autism. Autism is usually first
identified in children during the second year of life. The vaccine that
children receive closest to this time is MMR and thus some children develop or
are recognized as having autism shortly after receiving MMR. However, this
temporal association does not prove causation.
Andrew Wakefield, MD, and colleagues published a report in 1998 that
proposed an association between MMR and autism. They described 12 children
referred to their pediatric gastroenterology unit with diarrhea and abdominal
pain, as well as a history of normal development followed by a loss of acquired
skills. Eight of the children had autism. The onset of symptoms was associated
with MMR in six of the eight children with autism. When gastrointestinal
endoscopy was performed, seven out of the eight were found to have lymphoid
nodular hyperplasia. Wakefield hypothesized that the MMR vaccine introduced a
series of events, including colitis, intestinal inflammation, increased
intestinal permeability and absorption of encephalopathic proteins into the
bloodstream that enter the brain and cause autism.9
Figure 2. Perception of Vaccines
A graph illustrating the
changing perception of disease burden and vaccine safety. (Courtesy of
Robert T. Chen, MD from Chen RT. Safety of vaccines. In: Plotkin SA, Orenstein
WA, eds. Vaccines. Philadelphia, Pa: WB Saunders; 1999:1145.)
However, the behavioral symptoms preceded the gastrointestinal
symptoms in all cases, and ileal and colonic lymphoid hyperplasia occurs in
about 25% of children and is considered a normal variant. With a small case
series and the absence of a control group, the authors correctly concluded that
these cases “did not prove an association between measles, mumps, and
rubella vaccine and the syndrome described.”9 Epidemiologic
studies subsequently conducted in the United States and Europe have not found
an association.
A population-based study from the United Kingdom investigated the
incidence of autism before and after introduction of MMR vaccine in October
1998. Approximately 500 cases of autism were identified during the period
studied, with a steady increase in cases by year of birth. However, there was
no change in the trend after introduction of MMR vaccine, and no temporal
association between MMR vaccination and the onset of autism. The authors
concluded that their analyses did not support a causal relationship between MMR
and autism.10
In the United States, retrospective analyses of cases of autism and
MMR vaccine coverage rates among children in California born between 1980 and
1994 showed no apparent correlation between the vaccine and
autism.11 Although diagnoses of autism rose sharply in children
through the study period, there was no corresponding increase in MMR vaccine
coverage during those years.
A recent study provides the strongest evidence to date that the MMR
vaccine does not cause autism. This population based, retrospective cohort
study looked at all 537,303 children born in Denmark from January 1991 through
December 1998. MMR vaccine had been administered to 82% of children. Autism was
diagnosed in 316 children and an autistic spectrum disorder in 422. The
analysis showed no increased risk of autism or autistic spectrum disorders in
vaccinated children compared with unvaccinated children. Furthermore, there was
no association between the age at vaccination or the time since vaccination and
the development of autism.12
In 2001, after reviewing the available research on the MMR-autism
hypothesis, the IOM concluded that the evidence favored rejection of a causal
relationship between MMR and autism. The committee found no proven biological
mechanisms that would explain such a
relationship.13
Thimerosal and autism
As the evidence has accumulated that MMR does not cause autism,
anti-vaccine groups have switched the spotlight to thimerosal, a vaccine
preservative used in some vaccines since the 1930s that contains small amounts
of ethyl mercury. In 1999, the FDA concluded that some infants given
thimerosal-containing vaccines at multiple visits would receive cumulative
doses of ethyl mercury that exceed safety guidelines established by the
Environmental Protection Agency for methyl mercury, another form of organic
mercury. The American Academy of Pediatrics and the U.S. Public Health Service,
therefore, recommended that thimerosal-containing vaccines be reduced or
eliminated. This goal was established as a precautionary measure, as there was
no evidence of any harm caused by the low levels of mercury in vaccines.
Mercury is a known neurotoxin, and anti-vaccine proponents have
suggested a relationship between thimerosal and neurodevelopmental problems,
including autism, attention-deficit/hyperactivity disorder and speech and
language delay.
A review by the IOM concluded that the hypothesis that thimerosal
exposure through childhood vaccines has caused neurodevelopmental disorders is
not supported by clinical or experimental evidence, although there are
inadequate data to accept or reject a causal relationship.14 The
hypothesis has some biological plausibility and, therefore, research studies
are ongoing to assess if thimerosal use was associated with mild levels of
neurologic impairment. If thimerosal did cause autism, one would expect the
incidence of autism in the United States to decrease over the next few years
since thimerosal has been removed from all vaccines routinely given to
infants.
Perception
Vaccines are preventative so, by their very nature, nothing happens
when they are effective in preventing a child from dying or suffering
significant morbidity. In addition, because vaccines have been so effective,
the diseases they prevent are rare and are often no longer seen as threats.
Parents are not afraid of polio, diphtheria or measles because they have never
seen these diseases. As fear of the diseases declines, fears of adverse events,
whether real or only perceived, can predominate. Widespread concerns about
vaccine safety can lead to lower immunization levels and a resurgence of
disease. The resurgence of disease may then serve as a "reminder" of the
importance of immunizations (Figure 2).
Millions of children in the United States are vaccinated each year at
2, 4 and 6 months of age, so it should not be surprising that some children
will develop a cold, fever, diarrhea or seizures within a day or two of being
vaccinated. But sequence is not the same thing as consequence. An illness or
chronic disease that occurs after vaccination was not necessarily caused by the
vaccine.
Several years ago, a pediatrician told me a true story that
illustrates this point. Parents had brought their 2-month old daughter in for
her first set of immunizations. Because the parents had seen a Dateline
NBC story that suggested a link between pertussis vaccines and brain
damage, they did not want to have their daughter vaccinated against pertussis.
However, after the pediatrician spoke to the parents about what was known and
not known about pertussis, the pertussis vaccine and brain damage, the parents
agreed to have their daughter vaccinated.
As the vaccine was being drawn up into the syringe to be
administered, the child had a seizure. Had the vaccine been given 30 minutes,
three hours or a day earlier, the parents would have been convinced that the
vaccine caused the seizure. They would have been wrong.
If a child experiences an adverse reaction after receiving a vaccine,
physicians are encouraged to report it (through the Vaccine Adverse Event
Reporting System at www.vaers.org) but should not assume that the vaccine caused
the problem. Physicians need to remain educated about vaccines and vaccine
safety issues so that they can discuss concerns that parents have. Vaccine
myths and misperceptions should not interfere with our vaccination programs
– no child should needlessly suffer or die from a vaccine-preventable
disease. Parents want the truth, so we should give it to them —
immunizations are one of the most important things they can do to keep their
children healthy.
References
Centers for Disease Control and Prevention. Achievements in public
health, 1900-1999: Impact of vaccines universally recommended for Children
United States 1990-1998. MMWR. 1999;48:243-248.
Gangarosa EJ, Galazka AM, Wolfe CR et al. Impact of anti-vaccine
movements on pertussis control: the untold story. Lancet.
1998;351:356-361.
Gellin BG, Maibach EW, Marcuse EK. Do parents understand
immunizations? A national telephone survey. Pediatrics.
2000;106:1097-1102.
Offit PA, Quarles J, Gerber MA et al. Addressing parents’
concerns: do multiple vaccines overwhelm or weaken the infant’s immune
system? Pediatrics. 2002;109:124-129.
Stratton K, Wilson CB, McCormick MC, eds. Immunization
Safety Review: Multiple Immunizations and Immune Dysfunction.
Washington, D.C.: The National Academies Press; 2002.
Ascherio A, Zhang SM, Hernan MA, et al. Hepatitis B vaccination
and the risk of multiple sclerosis. N Engl J Med.
2001;344:327-332.
Confavreux C, Suissa S, Saddier P, Bourdes V, Vukusic S, and the
Vaccines in Multiple Sclerosis Study Group. Vaccinations and the risk of
relapse in multiple sclerosis. N Engl J Med.
2001;344:319-326.
Stratton K, Almario D and McCormick MC, eds. Immunization
Safety Review: Hepatitis B Vaccine and Demyelinating Neurological
Disorders. Washington, D.C.: The National Academies Press; 2002.
Wakefield AJ, Murch SH, Anthony A, et al. Ileal-lymphoid-nodular
hyperplasia, non-specific colitis, and pervasive developmental disorder in
children. Lancet. 1998;351:637-641.
Taylor B, Miller E, Farrington CP, et al. Autism and measles,
mumps, and rubella vaccine: No epidemiological evidence for a causal
association. Lancet. 1999;353:2026-2029.
Dales L, Hammer SJ, Smith NJ. Time trends in autism and in MMR
immunization coverage in California. JAMA.
2001;285:1183-1185.
Madsen KM, Hviid A, Vestergaard M et al. A population-based study
of measles, mumps, rubella vaccine and autism. N Engl J Med.
2002;347:1477-1482.
Stratton K, Wilson CB, McCormick MC, eds. Immunization
Safety Review: Measles-Mumps-Rubella Vaccine and Autism. Washington,
D.C.: The National Academies Press; 2001.
Stratton K, Gable A, McCormick MC, eds. Immunization Safety
Review: Thimerosal-Containing Vaccines and Neurodevelopmental Disorders.
Washington, D.C.: The National Academies Press; 2001.
