Context Individuals searching the Internet for vaccine information may find
antivaccination Web sites. Few published studies have systematically evaluated
Objectives To examine antivaccination Web site attributes and to delineate the
specific claims and concerns expressed by antivaccination groups.
Design and Setting In late 2000, using a metasearch program that incorporates 10 other
search engines, we reviewed and analyzed 772 links to find 12 Web sites that
promulgated antivaccination information. Analyzing links from these 12 sites
yielded another 10 sites, producing a total of 22 sites for study. Using a
standardized form, 2 authors (R.M.W., L.K.S.) systematically evaluated these
sites based on specific content and design attributes.
Main Outcome Measures Presence or absence of 11 Web site content attributes (antivaccination
claims) and 10 Web site design attributes.
Results The most commonly found content claims were that vaccines cause idiopathic
illness (100% of sites), vaccines erode immunity (95%), adverse vaccine reactions
are underreported (95%), and vaccination policy is motivated by profit (91%).
The most common design attributes were the presence of links to other antivaccination
sites (100%of sites), information for legally avoiding immunizations (64%),
and the use of emotionally charged stories of children who had allegedly been
killed or harmed by vaccines (55%).
Conclusion Antivaccination Web sites express a range of concerns related to vaccine
safety and varying levels of distrust in medicine. The sites rely heavily
on emotional appeal to convey their message.
Vaccines are considered one of the greatest achievements of biomedical
science and public health.1 However, during
the last few decades an increasingly vocal antivaccination movement has challenged
the safety and effectiveness of recommended vaccines.2,3
The extent of concern in the United States was highlighted by a national survey
that found that although the majority of parents supported vaccination, 25%
believed that too many vaccinations could weaken children's immune systems
and 23% believed that children get too many immunizations.4
Recent studies indicate that 66% of US adults (137 million) are now
online and that 80% of all adults online use the Internet to look for health
information.5,6 Furthermore, 52%
of those who have visited online health sites believe that "almost all" or
"most" of the health information they find online is credible.7
Individuals searching for vaccination information may find themselves visiting
antivaccination sites. This study explored the content and design attributes
of antivaccination sites that an individual might encounter doing a typical
Web search, with the goal of enhancing our understanding of concerns raised
on these sites.
Using the Netlingo Dictionary of Internet Words
(http://www.netlingo.com) and the Webopedia Online
Computer Dictionary of Internet Terms (http://www.pcwebopedia.com), we defined a "Web page" as a single html file or document viewed
on a Web browser and a "Web site" as a site (location) on the World Wide Web.
Each Web site contains a "home page," which is the first document users see
when they enter the site. Each site is owned and managed by an individual,
company, or organization.
A "link" (or "hyperlink") is an element in an electronic document that
links to another place in the same document or to an entirely different document.
Typically, clicking on a hyperlink will transport a user to another document
or section of the document.
Antivaccination Web pages were identified using Copernic 2000 v4.55a
(Copernic Technologies Inc, Sainte Foy, Québec), an Internet search
utility program designed to simultaneously submit searches on numerous search
engines. We used 10 search engines: AltaVista, EuroSeek, Excite, Google, GoTo.com, HotBot, Infoseek, Lycos, Yahoo, and All the Web FAST Search,
with up to 30 results returned on each engine for a maximum of 300 results
per search. Two of the investigators (R.M.W., L.K.S.) jointly conducted 4
searches between August 3, 2000, and September 3, 2000, using the keywords vaccine, vaccinate, vaccination, immunize, immunization, immunise, immunisation, anti-vaccination, anti-immunization, and anti-immunisation.
The initial searches identified 851 links to Web sites, of which 79
were invalid or duplicate links. The resulting 772 sites were reviewed together
by both searchers to select those for study based on the criteria below.
Inclusion and Exclusion Criteria
A Web site was considered for review if it contained content specifically
opposing vaccination for human infants or children. The following Web sites
were excluded: (1) online health/medical journals or newspaper sites, (2)
listservs or newsgroups containing online conversations, and (3) sites not
written in the English language. Two authors (R.M.W., L.K.S.) reviewed the
772 links, identifying 12 Web sites opposing childhood vaccinations. A secondary
survey of all links leading from the 12 sites to other antivaccination sites
identified 10 additional links resulting in a total of 22 sites for final
data extraction. Of the final 22 sites, there were 16 from the United States,
2 from the United Kingdom, 2 from Australia, 1 from New Zealand, and 1 from
France (text available in English).
Data extraction included 11 Web site content attributes (antivaccination
claims, Figure 1) modified from
the work of Leask and Chapman8 on the antivaccination
movement in Australia, from the US Centers for Disease Control and Prevention
criteria,9 and 2 items developed by the authors.
In addition, 10 design attributes (Figure
2) were identified based on criteria published by Kim et al.10
Only material present on the original Web site was evaluated. Links
to other sites were excluded. For each site, each content and design item
was classified as present or absent. Two authors (R.M.W., L.K.S.) reviewed
4 sites separately, with 100% interrater reliability. These authors reviewed
the 18 remaining sites jointly.
Content Variables: Antivaccination Claims
The total number of claims per site ranged from 2 to 11, with 18 (82%)
of the sites exhibiting 7 or more of the 11 claims. Two sites with the fewest
claims were created by medical researchers with publications in peer-reviewed
"Vaccines cause idiopathic illness." All of
the sites included content suggesting that vaccines cause idiopathic illnesses.
The most common illnesses ascribed to vaccination included: autism (specifically
from measles/mumps/rubella [MMR] and/or diphtheria/pertussis/tetanus [DPT]
vaccine), sudden infant death syndrome (SIDS), immune dysfunction, diabetes,
neurologic disorders (including seizures, brain damage, learning disabilities,
attention deficit disorder, antisocial behavior), and atopic disorders, including
allergic rhinitis, eczema, and asthma.
"Hot Lots" and "Increased Risk From Multiple Simultaneous
Vaccines." Two claims related to issues of vaccine manufacture and
administration. The first claim, that allegedly contaminated vaccination lots
(ie, "hot lots") are more likely to cause an adverse reaction, was addressed
by 12 (55%) of the sites. The second claim, that giving multiple vaccines
at the same time increases the risk of an adverse event, appeared on 11 (50%)
of the sites. A number of sites where this claim appeared cited 2 published
case reports that suggested that combined MMR vaccine was a risk factor for
autism.11,12 Several studies and
medical review panels that have not supported this hypothesis were not referenced.13-16
"Vaccines Erode Immunity" and "Immunity Is Temporary/Ineffective." Twenty-one sites stated that vaccinations eroded or harmed the immune
system, specifically inducing autoimmunity. A frequent concomitant claim was
that naturally occurring diseases helped the immune system, preventing illnesses
such as asthma and atopy, and that vaccinations interfered with this benefit.
One site included an antivaccination article written by a physicians' group
specializing in "family, environmental and preventive medicine" that cited
4 references in support of this idea,17-20
without mention of the opposing published data.21-23
Eighteen (81%) of the sites alleged that vaccines are ineffective or
produce temporary immunity.
"Adverse Vaccine Reactions Are Underreported."
Twenty-one (95%) sites argued that adverse vaccine reactions (or vaccine failure)
are underreported, but reasons given for underreporting varied. The most common
reason was that physicians fail to recognize delayed reactions as vaccine
related or fail to report them. Others argued that agencies involved with
vaccine production and regulation were purposefully covering up the truth.
"Diseases Have Declined" and "Homeopathy Alternative." Sixteen sites (73%) stated that prior to the use of vaccinations these
diseases had begun to decline due to improved nutrition and hygiene, and that
vaccines were given undue credit for these declines. Homeopathy, alternative
health, and natural methods of enhancing immunity, such as breastfeeding or
proper diet, were promoted on many of these sites. Homeopathy was also endorsed
as a means of reducing the severity of postvaccination reactions. Sites advocating
homeopathy were often associated with statements attacking Pasteur and the
germ theory of disease.
"Vaccine Policy Is Motivated by Profit." The
idea that vaccine policy is motivated by profit was found on 20 of the sites
(91%). The general thesis was that vaccine manufacturers make enormous profits,
which influences universal vaccination recommendations and promotes the cover-up
of vaccine adverse effects. More extreme arguments posited that physicians
are biased by financial inducements from vaccine manufacturers, especially
in the form of gifts or research grants.
"Violation of Civil Liberties." Seventeen (77%)
of the sites mentioned civil liberty concerns associated with mandated vaccination.
Electronic vaccine registries, designed to allow tracking of childhood immunizations,
were attacked as an example of "Big Brother" intruding into the lives of citizens.
"Use of Aborted Fetal Tissue." Seven (32%)
of the sites raised the fact that viruses grown from cell cultures of aborted
fetuses (lines MRC5 and WI-38) are used in varicella, rubella, and hepatitis
A vaccines.24 Antivaccination sites raise both
moral issues and concerns about adverse effects from injecting such materials
Figure 2 shows the frequencies
of the 10 design attributes we used to further characterize these sites. All
sites had links to other antivaccination sites. Ten (45%) of the sites displayed
links to authoritative provaccination sources such as the Centers for Disease
Control and Prevention. Stories of children harmed by vaccines were very common,
as was information on how to legally avoid vaccinations. Seven sites (32%)
displayed pictures of menacing needles, and 5 sites (23%) displayed pictures
of children allegedly harmed or killed by vaccine reactions.
This study systematically collected information on the content and design
attributes of antivaccination Web sites. Our results show that such sites
express a variety of claims that are largely unsupported by peer-reviewed
scientific literature. There were 3 broad themes expressed on the antivaccination
Web sites: concerns about vaccine safety and effectiveness, concerns about
governmental abuses, and a preference for alternative health practices. The
key concern relates to the perceived risk of disease, harm, or death when
a child receives a vaccine. Second, mandated vaccination is viewed as an unacceptable
infringement of personal choice and civil liberties. Furthermore, there is
a pervasive sense of distrust, expressed in beliefs that governmental oversight
bodies suppress reports of adverse vaccine reactions and collude with the
pharmaceutical industry to profit from vaccine sales. And third, alternative
health practices are valued over allopathic health care, and are believed
to obviate the need for vaccination. The arguments used on these sites are
not new: most were used in the 19th century by opponents of compulsory smallpox
Fifty-five percent of the sites provided personal accounts written by
parents who believed that their child was killed or permanently harmed by
vaccination, and almost one fourth of the sites included pictures of the affected
children. Such visual images of purported adverse consequences can be unsettling
to parents facing vaccination decisions. In social psychology terms, these
parents may be swayed by "false consensus bias," a tendency to rely on personal
experience as opposed to scientific evidence. In essence, an individual's
beliefs regarding vaccination are unduly swayed by personal and emotional
anecdotes to the exclusion of evidence. In contrast, the once overwhelmingly
apparent visual images of the benefits from vaccination have disappeared as
their respective diseases—such as polio—have disappeared.
Although this study did not formally evaluate the accuracy of medical
references provided on antivaccination Web sites, a separate review found
that sites that contain citations to scientific papers often misrepresent
their contents.26 Many claims we encountered
were supported by references from homeopathic or alternative medical literature.
Typically, arguments connecting vaccination to adverse effects were made using
the logical fallacy post hoc ergo propter hoc ("after
this, therefore because of this"), which mistakes association for causation.8 For example, since autism occurs in the first 2 years
of life when multiple vaccines are given, many anti-immunization proponents
conclude that vaccines cause autism. Although controlled studies do not support
this association, it remains an area of contention between public health authorities
and antivaccinationists, reflected in recent congressional hearings about
This study is limited by the dynamic nature of the Internet, where entire
Web sites appear and disappear or move to other "addresses" overnight. Defining
the content of a site is also a problem. On the Internet, a document on another
site, accessed by clicking on a link, is often no harder to reach than a document
on the original site. This study looked only at pages on the original site,
believing this implied more "ownership" of the material and provided a standardized
method of assessing each site. The study was limited to English-language sites;
therefore, the findings may not extend to antivaccination sites written in
Vaccination is not risk free, but most in mainstream medicine agree
that the benefits of vaccination outweigh the risks.29
While the majority of the public accepts immunization, it appears that increasing
numbers of parents are seeking philosophical exemptions from vaccination for
their children. For example, in Colorado the rate of philosophical exemptions
from vaccination rose from 0.87% in 1988 to 1.87% in 1998, with the rate of
religious exemption holding steady at about 0.2%.30
Although a few unimmunized individuals are most likely protected by herd immunity,
growing numbers of unvaccinated individuals could eventually pose a risk to
both themselves and society.31 We believe our
study findings can help direct research aimed at more effectively addressing
the concerns of individuals opposing childhood vaccination.
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