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Human Vaccines & Immunotherapeutics Volume 9, 2013 - Issue 8
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Review

The rise (and fall?) of parental vaccine hesitancy

Charitha Gowda Division of Infectious Diseases; University of Pennsylvania; Philadelphia, PA USA
&
Amanda F Dempsey Children’s Hospital Colorado; Denver, CO USACorrespondenceamanda.dempsey@ucdenver.edu
Pages 1755-1762 | Received 26 Feb 2013, Accepted 18 May 2013, Published online: 06 Jun 2013

Abstract

Parental vaccine hesitancy is a growing problem affecting the health of children and the larger population. This article describes the evolution of the vaccine hesitancy movement and the individual, vaccine-specific and societal factors contributing to this phenomenon. In addition, potential strategies to mitigate the rising tide of parent vaccine reluctance and refusal are discussed.

Introduction

A resurgence of outbreaks of vaccine-preventable diseases (VPDs), including measles and pertussis,Citation1-Citation5 has prompted renewed attention on how vaccine hesitancy can lead to the spread of infection and negatively impact public health. However, vaccine hesitancy is not a new phenomenon. Concern and controversy over the relative benefit vs. potential harm of vaccines have been long debated by the public, ever since the 18th century when Jenner’s use of the cowpox virus to provide immunity against smallpox first demonstrated the principle of vaccination.Citation6,Citation7 Over time, due to changes in the prevalence of VPDs, the ability to rapidly disseminate information (including supposed vaccine “controversies”) via traditional media and the internet, and the increasing number of vaccines now available or under development, there has been an evolution in the public’s understanding of vaccines and the predominant concerns that fuel vaccine hesitancy today.

In this article, we examine the increasing trend of parental vaccine hesitancy over time, the factors engendering vaccine doubt among “vaccine-hesitant parents” (VHPs), and potential strategies to address vaccine hesitancy when it arises. We focus specifically on vaccines recommended for children and adolescents, which require parental awareness and acceptance for vaccine administration.

Trends in Vaccine Hesitancy Over Time

Although coverage levels for most childhood vaccines remain high in the United States,Citation8,Citation9 numerous studies have documented that vaccine-related confidence has been decreasing among US parents over the past several years. In a national study of parents performed in 2000, 19% indicated they had “concerns about vaccines” whereas in a subsequent survey performed in 2009 this number had risen to 50%.Citation10,Citation11 Concurrent with the rise in parental vaccine hesitancy is the steady increase in non-medical vaccine exemptions that has occurred over the last several years.Citation12 In a 2010 National survey of physicians, 89% of respondents reported at least one vaccine refusal by a parent each month.Citation13

Vaccine hesitancy can take several forms. At its most severe, parents refuse all recommended vaccines. However, this viewpoint is relatively rare, adopted by only 1–2% of parents nationally.Citation11,Citation14-Citation16 Instead, delay or refusal of one or more specific vaccines is much more common. For example, in a national study performed by Gust et al. in 2003, 28% of parents reported vaccine hesitancy, of which approximately two-thirds delayed or refused only certain vaccines.Citation16 In a study by Freed et al. performed in 2009, 11.5% of parents nationally had refused at least one vaccine for their child, occurring most commonly with human papillomavirus and varicella vaccine, with 56% and 32% of vaccine-refusing parents reporting refusal of these specific vaccines, respectively. In a 2010 study by Dempsey et al., H1N1 and seasonal influenza vaccine were the most commonly refused vaccines, reported by 86% and 76% of vaccine-hesitant parents, respectively. Another form of vaccine hesitancy is when parents elect to have all vaccines provided to their children on delayed schedule. This alternative schedule is less common that refusing or delaying only specific vaccines, but more common that complete vaccine refusal.

Public Health Impact of Vaccine Hesitancy

With the rise of vaccine hesitancy, increasing numbers of children are being put on “alternative” vaccine schedules that differ from the recommended immunization schedule. This results in unnecessarily increased periods of “risk exposure” for contracting a VPD.Citation14 Consistent with this, the incidence of several vaccine-preventable diseases has been on the rise. In 2008 alone, the US saw 140 measles cases, more than twice the average number of annual cases from 2000 to 2007.Citation17 According to the Centers for Disease Control and Prevention (CDC), this increase was not due simply to greater numbers of imported cases but also to greater viral transmission within communities of unvaccinated individuals—99 of 106 US-born cases with known vaccination histories were unvaccinated.Citation18 Historically significant outbreaks of pertussis, mumps and rubella have also occurred in the US, largely within under- or unvaccinated populations.Citation1,Citation17-Citation21

Other countries have witnessed similar outbreaks of vaccine-preventable diseases associated with increasing concerns about vaccine-related safety. Devastating outcomes were seen in Nigeria, for example, where concerns about polio vaccination safety led to a suspension of polio immunization activities in 2003 and 2004, with a resultant rise in cases.Citation22 VPDs have resurged in countries of all stages of development. Similar to the US, other developed countries in western Europe and Australia have seen measles, mumps, rubella or pertussis outbreaks in recent years.Citation23-Citation26 After publication of Wakefield’s now discredited hypothesis that the MMR vaccine is associated with autism,Citation27,Citation28 MMR vaccination levels sharply dropped in many European countries and remain below those seen prior to 1998;Citation29 as a result these countries have seen a rise in cases of measles.Citation25,Citation30 Outbreaks of rubella and mumps have been documented in communities with low-vaccination rates in the Netherlands.Citation24,Citation26

Defining Vaccine Hesitant Parents

At least one in four parents expresses serious reservations about the recommended childhood vaccine schedule and can thus be broadly categorized as a VHP.Citation16,Citation31 Yet, vaccine-hesitant parents are actually comprised of a widely heterogeneous group, displaying a variety of attitudes and beliefs toward specific vaccines, vaccine schedule preferences and vaccination intentions and behaviors. Because of this, VHPs may be best understood as falling within a spectrum, ranging from those vehemently opposed to all vaccines to those who demonstrate universal support for vaccines ().

Figure 1. Continuum of parental vaccine acceptance.

Figure 1. Continuum of parental vaccine acceptance.

Numerous studies have addressed the heterogeneity of VHPs by attempting to categorize such parents into “subsets” based on their specific beliefs or level of vaccine hesitancy. For example, Gust et al.Citation32 used data from surveys of parental attitudes and beliefs regarding immunizations to generate 5 categories of VHPs with similar attitudinal subsets. These included “Immunization Advocates,” “Go Along to Get Alongs,” “Health Advocates,” “Fence-sitters” and “Worrieds.” In a different framework developed by Leask et al.,Citation33 both vaccine hesitant and non-hesitant parents were classified into five groups regarding their immunization beliefs. These groups ranged from the “Unquestioning Acceptor” to the “Refuser,” with three interim groups describing VHPs: “Cautious Acceptors,” “Hesitants,” “Late/Selective” vaccinators.

More recently, Opel et al. have developed a questionnaire to classify vaccine-hesitant parents into different “levels” of vaccine hesitancy and validated the predictive capacity of these categorizations to reflect future vaccination behaviors.Citation31,Citation34 Such a tool will be extremely helpful for developing interventions so that the content and presentation (e.g., gain- vs. loss-framed messages, personal narratives vs. fact lists) of vaccine-related information provided can match each parent’s specific vaccines concerns, knowledge and beliefs, and information preferences. The need for this type of “matching” is supported by a recent study of vaccination barriers among MMR vaccine-hesitant parents. This study demonstrated that providing information to counteract MMR vaccine-specific concerns had varying degrees of influence on parents in their decision-making for the vaccine depending on their relative “level” of vaccine-hesitancy.Citation35

Factors Affecting Vaccine Hesitancy

Given the diversity observed among VHPs, it can be helpful to use a framework to understand the multiple “levels” of factors that influence vaccine confidence and acceptance (). Understanding how vaccine-specific, individual-level, and “external” (i.e., societal, familial) factors impact vaccine hesitancy will likely be important for developing effective interventions in the future to mitigate this problem. While these factors are presented separately, it is important to acknowledge their interrelatedness. For example, external factors such as media potrayals of vaccine controversies can drive changes individual knowledge and beliefs.

Figure 2. Framework for understanding the different types of factors influencing parental vaccine hesitancy.

Figure 2. Framework for understanding the different types of factors influencing parental vaccine hesitancy.

Vaccine-specific beliefs that impact vaccine hesitancy

Vaccine-specific factors impact vaccine decision-making by moderating perceptions about the relative risks and benefits to vaccinating vs. not vaccinating. Concerns about the immediate or short-term side effects of vaccines are significant drivers of vaccine delay and/or refusal. In a study of parents of young children aged 6 y or less, common concerns identified by parents included pain during injections and fevers after vaccination.Citation36 Qualitative studies have also suggested that vaccine-hesitant parents are significantly concerned about the immediate side effects of vaccines. For example, Shui et al.Citation37 conducted focus groups of African-American mothers and found that a majority expressed reservations about potential adverse reactions from vaccines such as redness, swelling or pain at the injection site. The discomfort associated with vaccinations remains a significant barrier to vaccination, even as children age. Parents of adolescents commonly report that fear of needles and the associated pain are important considerations that influence their intention to vaccinate their children.Citation38

Parental concerns about vaccine safety extend beyond the immediate, localized reactions to fear of potential, long-lasting complications, including neurologic conditions. Although the purported association between the measles vaccine and autism has been scientifically disproven,Citation39,Citation40 some parents continue to express reservations about the MMR vaccine causing this problem.Citation36,Citation41-Citation43 The influenza vaccine is another example, where some parents are worried that this vaccine may lead to Guillain-Barre syndrome although numerous studies of current formulations of the influenza vaccine have not been able to validate such an association.Citation44 Other parents express reservations about vaccine safety in general, emphasizing the potential risks of vaccination over those of the disease, reflecting a well-established human propensity for omission bias (i.e., preferring the consequences of not doing something to the consequences of doing something).Citation42,Citation45

Additional concerns about vaccine safety focus on the number and timing of recommended vaccines. Multiple vaccines have been newly introduced and adopted into the recommended childhood vaccination schedule including rotavirus, Tdap, meningococcal and HPV vaccines.Citation46 With additional new vaccines in the pipeline, the number of recommended vaccines is slated to grow in the future. This has alarmed parents who fear that too many vaccines, especially in a short period of time, could be harmful for their children. Specifically, some parents are concerned about the cumulative pain and discomfort experienced by children who receive multiple shots at once. Others worry about the potential health risks of receiving multiple vaccinations during one clinic visit, wondering whether the body can handle so many different antigens at once. Additionally, parents question whether the immune system may become overloaded by receipt of all the recommended vaccines during early childhood.Citation36,Citation37 Given these concerns, there is clearly a need for greater dissemination of information about vaccine development and safety monitoring.Citation47

Perceptions about vaccine efficacy are an integral factor in the vaccination decision for VHPs and can be broken down into two components: (1) perceived susceptibility to disease and (2) perceived efficacy of vaccine-induced immunity. The overwhelming success of vaccination efforts in drastically reducing the incidence of VPDs over the last century has resulted in diminished exposure to VPDs and associated complications. As a result, parents do not perceive such illnesses to necessarily be significant health threats. For example, the elimination of measles as an infection endemic to the US as of 2000Citation48 has led parents to question whether there is a continued need for the measles vaccine. With overall high immunization levels in the US, some parents perceive that there is a diminished need for their children also to be vaccinated, assuming they will benefit from herd immunity.Citation42 Vaccine doubts among VHPs are further fueled by the resulting imbalance between decreasing levels of perceived disease susceptibility and increasing concerns about vaccine safety.

Among vaccine-hesitant parents, there is significant concern over the relative efficacy of vaccine-induced immunity vs. immunity obtained through the natural course of disease, with some parents preferring their children obtain immunity “naturally” as opposed to via vaccination.Citation49-Citation51 There are several possible reasons fostering this belief. First, personal experience with a limited form of the disease may have led parents to believe that disease-related risks are low and relatively inconsequential. This is particularly true for the varicella vaccine, as many parents recall having had varicella during childhood and generally lack awareness of the potentially serious complications associated with the disease. Interestingly, some parents also cite a preference for naturally acquired infection as a reason for not giving their children the measles-containing vaccine. In this case, lack of personal experience with the disease may lead parents to underestimate the risk of devastating complications from infection.Citation37,Citation43 This preference for natural immunity indicates a lack of understanding about vaccination principles, suggesting a potential target area for future educational campaigns.

Finally, uncertainty about vaccines is fueled by ongoing and frequent changes to the childhood vaccine schedule, both by the Advisory Committee on Immunization Practices (ACIP) on a national scale, and by physicians within local practices. For example, immunization delays or changes to vaccine recommendations due to vaccine shortages, as seen during the Hemophilus influenza Type b conjugate vaccine shortage from 2007 to 2008,Citation52 can raise doubts among parents about the importance of strictly adhering to the recommended vaccine schedule. As a result, physicians may have a more challenging time explaining why vaccines should not be delayed due to parental preference. Furthermore, alterations to vaccine recommendations may confuse parents or raise concerns about what prompted the changes. For example, some parents of adolescents raised doubts about why the influenza vaccine was now being recommended for adolescents when previously it had not been.Citation38 Thus, it is imperative that physicians and public health professionals inform parents not only about changes to vaccine schedules, but also why these new recommendations are being adopted, so as to provide an opportunity for newly arising concerns to be discussed

Individual-level factors

Individual-level factors such as socioeconomics, race, and education level directly impact each person’s concept of the risks and benefits of vaccination vs. the risks and sequelae of a VPD. Socioeconomic factors appear to have conflicting associations with parental immunization acceptance, which could reflect differences in underlying beliefs about vaccines that differ by socioeconomic strata. Parents of lower-income brackets have been shown in some studies to have greater levels of concern about the safety and necessity of vaccines as compared with those of higher income.Citation31,Citation53-Citation55 For example, in one national survey of parents of young children, those in the lowest income category reported nearly 50% higher levels of agreement that vaccinations are associated with serious side effects and significantly lower levels of agreement that their children are susceptible to VPDs and that vaccines can be protective against VPDs than higher income parents.Citation54 In fact, when US parents who oppose compulsory vaccination were studied, lower income was the only socio-demographic characteristic independently associated with vaccination opposition.Citation55 In contrast however, Opel et al. showed that while parents with household incomes > $75,000 were 2-fold more likely to be unconcerned about serious vaccine-related adverse reactions than those with lower incomes, the opposite effect was found when examining the association between income and attitudes about vaccine safety.Citation31 Parents in the higher income bracket were more than two times as likely as parents from lower income brackets to be concerned that shots might not be safe. The apparent contradiction could be related to differing perceptions of what “vaccine safety” means among parents from different socioeconomic backgrounds. For example, parents in high-income brackets may relate “vaccine safety” to concerns such as autism or autoimmune disease, but “vaccine-related adverse events” to consequences like fever or soreness. In contrast, parents in lower income brackets might interpret these terms differently. Further study is needed to better understand what terms like “side effects,” “safety” and “adverse events” mean to different populations of people so that effective public health messages can be crafted.

Level of parental education has also been implicated as contributing to vaccine hesitancy. Several studies demonstrate that parents with less formal education have greater distrust in the medical community, express more concerns about vaccine safety and have less belief in the necessity and efficacy of vaccines.Citation31,Citation50,Citation53,Citation54,Citation56 Gust et al.Citation56 found that parents with less than 12 y of education were more likely to report not having enough vaccination information, compared with parents with some graduate school education. This, combined with greater distrust in the medical community, may lead these parents to seek out alternative sources of information such as family members, other parents in the community, or the media.Citation41,Citation42 The increasing prevalence of anti-vaccination messages presented in these outlets likely contributes further propagating parental vaccine hesitancy.Citation57-Citation59 However, like income, there appears to be a conflicting influence of education on vaccination attitudes. For example, Opel et al. found that parents with higher levels of education were nearly four times as likely to be concerned about the safety of vaccine than those from lower education levels.Citation31 Similarly, Smith et al. found that refusal of all childhood vaccines was more common among college educated parents than those with lower levels of education.Citation60

While some studies have suggested that African-American children have lower immunization coverage levels compared with other race groups,Citation61-Citation63 more recent data have not shown significant differences in national vaccine coverage levels by racial/ethnic groups, particularly after adjustment for poverty status.Citation8,Citation9 However, some studies have shown that race/ethnicity is associated with differential levels and types of immunization concerns.Citation36,Citation39,Citation50,Citation51 For example, in a nationally representative sample of parents of children ≤18 y where parents were categorized by their level of immunization safety concern, very concerned parents were more likely to be black or Hispanic compared with whites.Citation53 Prislin et al.Citation50 showed that African-Americans endorsed weaker beliefs in the protective value of vaccines, resulting in decreased vaccine acceptance when compared with Hispanics and white Americans. Interestingly, Freed et al.Citation43 found in a national survey of parents that Hispanics, despite being more concerned about the serious adverse effects of vaccines, were also more likely than comparator groups to follow their doctors’ vaccine recommendations, and less likely to have ever refused a vaccine. This latter finding supports the observation that simply expressing vaccine-related concerns does not directly translate to decreased vaccine administration. . Given these concerns, there is clearly a need for greater dissemination of information about vaccine development and safety monitoring.Citation61,Citation62

External factors

External factors moderate vaccine decision-making by shaping societal norms which, in turn, can impact individuals’ perceptions about disease risk and prevention (either positively or negatively). Physicians overwhelmingly remain one of the most important sources of information for parents about their children’s health. Numerous studies demonstrate that the strength of recommendations and emphasis placed on immunizations by the provider can influence a parent’s confidence in (and thus acceptance of) vaccines.Citation54 Smith et al.Citation65 showed that parents who reported that their vaccination decisions were positively influenced by healthcare providers were also more likely to believe that vaccines were safe. However, providers who share vaccine-related concerns or place less importance on vaccines may transmit these beliefs to their patients and families. Salmon et al.Citation66 compared the vaccination knowledge and practices between primary care providers of fully vaccinated children and those of children who received exemptions from school immunization requirements. Compared with fully vaccinating providers, those who cared for exempt children had significantly increased concerns about vaccine safety and perceived less benefit from vaccines.Citation66

“Quality” of the relationship between parents and the health care provider also appears to be important. Gust et al.Citation54 found that parents with lower levels of trust in their child’s doctor also had lower confidence in the safety of vaccines.Citation54 Level of trust is an important distinguishing factor between parents who adamantly oppose vaccines (i.e., “vaccine refusers”) vs. VHPs. “Refusers” generally report greater distrust of healthcare providers and place less emphasis on providers’ recommendations when making healthcare decisions. In contrast, VHPs appear to align more with “vaccine acceptors,” expressing a willingness to listen to providers’ healthcare recommendations.Citation42,Citation67 Given this, healthcare providers could help restore vaccine confidence among VHPs by promoting healthy lines of communication with and offering multiple avenues for information gathering for patients and families.

Vaccine confidence and immunization decisions are also driven by perceived social norms or collective values. Many parents rely on other parents or family members as sources of vaccine-related information.Citation58 Specifically, decisions to immunize are mediated in part by perceptions of what other parents in the community are doing.Citation68-Citation70 Vaccine concerns endorsed by a small but highly vocal subset of VHPs may heighten vaccine hesitancy among other parents in the community, as is supported by studies demonstrating geographic clustering of non-medical exemptions to school-required vaccines.Citation71 Additionally, media including print, television and the internet, can help inform people about current societal practices, and the increased prevalence of concerns, fears and misinformation about vaccines. Propagation of “fear stories” likely has contributed to the growth of vaccine hesitancy in the US and internationally.Citation57-Citation59,Citation72 It is important to note, however, that the impact of collective values can be bidirectional - parental decisions to vaccinate their children can be positively influenced by the desire to be a “good parent.”Citation37

Finally, public policies such as school mandates and the ease or difficulty with which exemptions to these mandates can be obtained also appear to influence vaccine acceptance. School requirements significantly increase vaccine coverage levels, presumably by swaying some “Fence Sitters” toward vaccinating. As an added benefit, mandates for one vaccine may also result in a “spill-over effect” to improve vaccination levels for other, non-mandated vaccines.Citation73-Citation75 Closely related to the effectiveness of school mandates is the ease with which exemptions for such mandates can be obtained. Rota et al. demonstrated that at a state level, greater difficulty in obtaining non-medical vaccine exemptions was inversely associated with the proportion of children who had such an exemption filed.Citation76

Strategies to address vaccine hesitancy

Clearly, parental vaccine hesitancy is a growing problem with a significant public health impact. As described above, challenges to maintaining adequate vaccine coverage include overcoming negative vaccine- and individual-specific attitudes and beliefs amidst a continual barrage of external factors such as vaccine controversies and evolving vaccination schedules that can also affect vaccination acceptance. While strategies such as enforcing school mandates for immunization, minimizing policies that promote non-medical exemptions, and maintaining public health and financial support for vaccination have a positive impact on vaccination rates, additional, novel strategies are also needed to counteract the growing negativity of parental vaccination attitudes.

Tailoring information

One mechanism that shows promise for mitigating the effects of negative vaccine- and individual influences is the use of tailored educational materials. Tailored materials target each individual’s unique experiences, beliefs and attitudes about vaccination, which can result in perceptions that the information provided is more relevant, and thus more trustworthy and influential.Citation77 Tailored messaging approaches have been shown across diverse populations and health issues to be superior to non-tailored information for improving compliance with recommended health behaviors.Citation77-Citation83 The few studies have that used this approach with regard to vaccine hesitancy suggest it may be similarly effective. For example, in one study of 80 MMR-vaccine hesitant parents, those who received a website that was tailored to their specific attitudinal barriers about the vaccine were significantly more likely to have positive intentions for their child to receive the MMR vaccine in the coming year than those who received untailored information.Citation84 Similar results were found in second study that used the same methodology and comparison groups, but targeted mothers with concerns about HPV vaccination.Citation85 Finally, Gust et al. developed a series of educational brochures that were reviewed by “Fencesitter” and “Worried” mothers. Based on their differential feedback, separate brochures for each of these groups were subsequently developed so that the information presented matched the beliefs and concerns prominent among mothers in each group. Assessment of the revised, and now targeted (i.e., developed specifically for a population subgroup), versions of the brochures were significantly more acceptable to both groups of mothers than the original, generic, untargeted versions.Citation86

Finding an Immunization Champion

Media have played a large role in enforcing and disseminating views related to vaccine hesitancy and refusal.Citation87-Citation93 Within this context, the anti-vaccine movement has benefited from the participation of several notable celebrities that have actively propagated anti-vaccination messages. Their success can be attributed to a fundamental concept from social marketing – namely that messages are more influential and acceptable when the “messenger” is perceived as likeable, trustworthy and working toward the same goal as the intended audience for the message.Citation94 Indeed, in a 2009 national study of parents, 24% indicated they trusted celebrities “some” and 2% “a lot” for providing vaccine safety information.Citation95 Unfortunately, the pro-vaccination movement has not received endorsements by similarly influential celebrities, which could do much to bolster the public’s views about the necessity and safety of childhood vaccines by reiterating social norms that are more accepting of vaccination.

Vaccine developments

Additional strategies to minimize vaccine hesitancy could target vaccine development and administration. For example, finding ways to further combine vaccine antigens into a single vaccine dose could allay VHP’s fears about “too many shots overwhelming the immune system.” Implementing evidence-based pain control techniques could minimize VHP’s reluctance for vaccination because of the pain associated with vaccines. For certain vaccines, possible changes to the vaccine administration route and schedule may further address VHPs concerns. For example, the development of intranasal or oral vaccines may further minimize concerns about pain and injection-site side effects. In addition, studies are underway currently examining the efficacy of 2 doses of HPV vaccine instead of 3,Citation96-Citation98 and some clinicians are interested in the possibility of giving HPV vaccines earlier in childhood as a way to minimize its association with sexual activity. As additional vaccines are added to the recommended schedule in the future, it may become increasingly important to consider how to leverage factors such as these to address the concerns of VHPs.

Conclusion

Parental hesitancy for recommended childhood vaccines is a growing public health concern influenced by factors at the personal, vaccine and environmental levels. While some strategies to mitigate the trend of increased vaccine hesitancy have been identified and are already in place, additional interventions are needed - particularly to combat the growing trend of negative public and parental attitudes and unjustified fears about vaccines. Promising approaches include developing information technology to provide tailored immunization education materials that match each person’s unique needs, finding immunization champions that can resonate with parents on a personal level, and leveraging characteristics of the vaccine or the vaccination schedule to minimize the concerns of vaccine hesitant parents.

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

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