How Positive and Negative Blogs Influence Vaccine ...

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Health Communication, 27: 829–836, 2012 Copyright © Taylor & Francis Group, LLC ISSN: 1041-0236 print / 1532-7027 online DOI: 10.1080/10410236.2012.661348

HPV Vaccine Information in the Blogosphere: How Positive and Negative Blogs Influence Vaccine-Related Risk Perceptions, Attitudes, and Behavioral Intentions Xiaoli Nan and Kelly Madden Department of Communication University of Maryland

This research examines the impact of exposure to online blogs about the human papillomavirus (HPV) vaccine on vaccine-related risk perceptions, attitudes, and behavioral intentions. In a controlled experiment (N = 341), college students were exposed to either a negative blog post about the HPV vaccine or a positive one. Compared to the control group, participants who had viewed the negative blog perceived the vaccine as less safe, held more negative attitudes toward the vaccine, and had reduced intentions to receive the vaccine. In contrast, exposure to the positive blog did not alter any vaccine-related risk perceptions, attitudes, or intentions. Implications of the findings for online vaccine risk communication are discussed.

The Internet has become one of the most popular places for people to seek health-related information (Pew Research Center, 2009). A Pew Research Center (2009) study shows that the majority of those seeking health-related information online access user-generated content, such as online news groups and blogs. These online sources, however, do not always provide accurate information about health-related topics. In fact, research has found that online materials provide potentially dangerous suggestions related to health concerns, especially in the context of vaccination (e.g., Kata, 2010; Wolfe & Sharp, 2005; Wolfe, Sharp, & Lipsky, 2002). The antivaccination movement has taken advantage of the Internet as a place to disseminate information to a large number of people through an inexpensive means (Zimmerman et al., 2005). The rise of antivaccination movements has corresponded with falling rates of immunization, which have led to outbreaks of vaccine-preventable illnesses (Gangarosa et al., 1998), most recently measles (USA Today, 2011) and pertussis (Forbes, 2010). Online antivaccination messages protest against the administration of long-standing vaccines as well as newer vaccines, such as the vaccine approved to prevent infection with the human papillomavirus or HPV. Correspondence should be addressed to Xiaoli Nan, PhD, Assistant Professor, Department of Communication, University of Maryland, 2105A Skinner Building, College Park, MD 20742-7635. E-mail: [email protected]

HPV is the most common sexually transmitted infection in the United States, affecting approximately 6 million people each year (Centers for Disease Control and Prevention [CDC], 2009). Persistent infections with highrisk HPVs are the primary cause of cervical cancer, and infections with low-risk HPVs cause genital warts. Fortunately, the widespread use of Pap smears has significantly alleviated the severe consequences of HPVs through early detection of HPV infection, cervical cancer, or precancerous lesions. The HPV vaccine, on the other hand, protects against the two HPV types that cause 70% of cervical cancers (CDC, 2011a), thus dramatically reducing the costs associated with treatments. Because the HPV vaccine does not protect against all cervical cancers, it is recommended that Pap smears continue to be used, even in women who have been vaccinated against HPV, to achieve maximum protection from this deadly disease. There are currently two HPV vaccines licensed by the Food and Drug Administration (FDA): Gardasil (a quadrivalent vaccine) and Cervarix (a bivalent vaccine). Both vaccines are administered as a three-dose series. According to the CDC (2011b) guidelines, “Either HPV vaccine is routinely recommended for 11- or 12 year-old girls. The vaccine series can be started beginning at age 9 years. Catch-up vaccination is recommended for 13- through 26 year-old females who have not completed the vaccine series . . . the 3-dose series of quadrivalent HPV vaccine may be given to

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males aged 9 through 26 years to reduce their likelihood of acquiring genital warts.” Previous research has explored content contained on general antivaccination websites (Davies, Chapman, & Leask, 2002; Kata, 2010; Wolfe et al., 2002), as well as online information specifically related to the HPV vaccine (Habel, Liddon, & Stryker, 2009; Keelan, Pavri, Balakrishnan, & Wilson, 2010). However, few studies have examined how online vaccine information, especially user-generated content, might affect vaccine-related risk perceptions, attitudes, and behaviors. User-generated content such as blog posts has the potential to induce interpersonal communication that may affect behavioral outcomes and, additionally, blog posts themselves may be considered forms of interpersonal communication online that reinforce social norms or group views related to vaccination (Southwell & Yzer, 2007; Southwell & Yzer, 2009). With more and more people turning to the Internet and online user-generated content for healthrelated information, it seems imperative to understand the potential effects of being exposed to such content. People may be especially vulnerable to online antivaccination messages when making decisions about newer vaccines, as they have less knowledge and feel greater uncertainty about these vaccines. Additionally, if a vaccine is not mandated by the government, whether or not to receive the vaccine becomes a decision for the individual, which makes it more likely for online misleading information to influence vaccine uptake. The HPV vaccine is both new and not associated with widespread mandate programs.1 This study then seeks to examine how exposure to online blog entries, either supporting or in opposition to the HPV vaccine, might influence vaccine-related risk perceptions, attitudes toward HPV vaccination, and intentions to receive the vaccine.

LITERATURE REVIEW Online Information About Vaccination Analyses of vaccine information online in general have uncovered an abundance of opposition to vaccines. Research has shown that antivaccination websites focus on the danger and ineffectiveness of vaccines (Davies et al., 2002; Kata, 2010; Wolfe et al., 2002; Zimmerman et al., 2005). For example, vaccines are demonized as pollutants responsible for disorders such as sudden infant death syndrome and autism, illnesses such as cancer and AIDS, and even social concerns such as falling literacy rates and violent behavior (Davies et al., 2002). Antivaccination websites often include parental narratives that tell of children being harmed by vaccines (Davies et al., 2002; Kata, 2010). In these personal stories, avoiding vaccination was portrayed as the

best way to protect children and to be a responsible parent (Kata, 2010). Additionally, antivaccination websites have argued that a natural lifestyle is the best solution for disease prevention (Davies et al., 2002). Websites in opposition to vaccines also present information related to civil liberties and conspiracy theories. The most prevalent civil liberties concern revealed in Kata’s (2010) analysis was parental rights, which are said to be infringed upon when parents are not allowed to choose how to care for their children. Similarly, Wolfe et al. (2002) found that antivaccination websites concentrated on vaccine mandates and governmental intrusion into the lives of citizens. Several studies found that antivaccination websites made accusations of cover-ups or conspiracies by pharmaceutical companies, physicians, or government officials (Davies et al., 2002; Kata, 2010; Wolfe et al., 2002). Studies specifically examining online content related to the HPV vaccine have found both positive and negative information (Ache & Wallace, 2008; Habel et al., 2009; Keelan et al., 2010; Madden, Nan, Briones, & Waks, in press). For example, Habel et al. (2009) analyzed Internet news articles on the HPV vaccine during the summer of 2006, immediately following the licensure of the first HPV vaccine, Gardasil, and found that about half of the online news articles were neutral toward the vaccine, one-third were positive, and the rest were negative. An additional means of presenting information online is through social networking sites or blogs. Keelan et al. (2010) analyzed unique MySpace blogs that mentioned the HPV vaccine in May 2008. The study revealed that about half of the blogs were positive toward the vaccine and nearly half were negative toward the vaccine. The presentation of HPV vaccine information online has also extended from the written word to user-generated videos on the popular video-sharing website YouTube. Ache and Wallace (2008) analyzed unique YouTube videos related to the HPV vaccine. The study found that the vast majority of the videos portrayed the HPV vaccine in a positive manner and the remainder depicted the vaccine negatively. A more recent study, however, revealed that the tone of YouTube videos related to the HPV vaccine may have shifted since Ache and Wallace’s study, which was conducted in 2008. This updated study, conducted in 2011, found that about half of the YouTube videos related to the HPV vaccine were negative in tone, one-third were positive in tone, and the remainder were either neutral or ambiguous (Briones, Nan, Madden, & Waks, in press). Nevertheless, the difference that emerged between the more recent study and Ache and Wallace’s study may be explained by the use of different coding schemes, rather than by a substantive shift in tone regarding the HPV vaccine on YouTube. Effects of Online Information About Vaccination

1 As of October 2011, Washington, DC, and the state of Virginia are the only two states/districts that have a school-based HPV mandate program.

Although several studies have provided analysis of online information about vaccination, with a few exceptions,

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limited research has examined how online content about vaccines might affect vaccine-related risk perceptions, attitudes toward vaccines, and intentions to receive vaccines. Scholars have argued that health communication researchers will gain less from continued analyses of content and more from research on the actual influence of the obtained information on perceptions of vaccination (Betsch, 2011). Cross-sectional survey research has suggested that information about vaccination on the Internet may affect a person’s decision to get vaccinated. A study of pregnant women in Quebec (Farbey, Gagneur, & Pasquier, 2011) found that those who visited mainstream websites for information about vaccination were less likely to receive a vaccine for H1N1, a novel strain of influenza, than those who consulted with medical professionals. Results of a quasiexperiment conducted by Kortum, Edwards, and Kortum (2008) demonstrated that when people are presented with antivaccination messages or misinformation about vaccination they retain this information. The study found that after browsing the Internet for information related to vaccine safety, high school students left the experiment with significant misconceptions about vaccination. Research has only begun to address the effects of exposure to online vaccine information using a true experimental paradigm. Betsch, Renkewitz, Betsch, and Ulshöfer (2010) took an initial step in this direction with an experiment testing whether vaccine-critical websites raised perceptions of vaccine risk and altered intentions to get vaccinated. They found that browsing antivaccination websites for a brief period of time decreased risk perceptions of omitting vaccines and in turn decreased intentions to vaccinate. Exposure to vaccine-critical information online also increased participants’ perceptions of the risk of vaccinating. Betsch et al. concluded that the Internet is increasingly important in delivering health-related information. At the same time, the Internet provides large amounts of misleading information about alleged adverse vaccination effects, and the potential detrimental impact of such information needs to be systematically examined. To address the research gaps, our study seeks to investigate in an experiment how negative and positive online blogs about the HPV vaccine might influence vaccine-related risk perceptions, attitudes, and behavioral intentions. Given limited prior empirical evidence, our study is guided, first, by research questions that ask about the impact of exposure to negative and positive blogs (RQ1 and RQ2). Because the HPV vaccine has been primarily promoted as the vaccine that prevents cervical cancer (a women’s health issue), females, compared to males, may find the vaccine to be more personally relevant and thus hold greater motivation to process HPV vaccine-related information. More in-depth message elaboration may result in greater impact of relevant message features (e.g., positive vs. negative framing of information) on attitude change (Maheswaran & Meyers-Levy, 1990). Given the lack of prior empirical evidence, however,

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we explore possible gender effects on responses to online blogs about the vaccine with a research question (RQ3). RQ1: What impact does exposure (vs. nonexposure) to a negative online blog about the HPV vaccine have on individuals’ vaccine-related risk perceptions (i.e., perceived vaccine efficacy, perceived vaccine safety), attitudes toward HPV vaccination, and intentions to vaccinate? RQ2: What impact does exposure (vs. nonexposure) to a positive online blog about the HPV vaccine have on individuals’ vaccine-related risk perceptions (i.e., perceived vaccine efficacy, perceived vaccine safety), attitudes toward HPV vaccination, and intentions to vaccinate? RQ3: Will the impact of exposure to positive and negative online blogs on HPV vaccine-related risk perceptions, attitudes, and behavioral intentions be different for males and females?

METHOD Participants Undergraduate students from a large East Coast university were invited to complete an online survey in exchange for course credit. The sample was composed of 341 individuals, including 107 men and 234 women with a mean age of 20 (SD = 2.50). Whites constituted 63.9% of the sample, Blacks 10.9%, Hispanics 4.4%, Asians 16.7%, and other 4.1%. Design and Procedure Participants first visited a webpage that provided general study information. Informed consent was obtained as participants clicked the “agree to participate” button at the bottom of the informational webpage. The button was also programmed such that participants were randomly directed to three websites corresponding to the three experimental conditions (negative blog, positive blog, and control). Upon entering the study website, participants first responded to a series of preliminary questions, including those about their demographic background, awareness of HPV/HPV vaccines, general beliefs and attitudes toward vaccines/vaccination, and perceived susceptibility to and severity of HPV. Next, participants in the treatment groups (negative blog and positive blog) were told that they were about to see an article posted by an online blogger about the HPV vaccine and were instructed to read the blog carefully (see later description of the blogs). After participants finished reading the blog, they proceeded to complete a postintervention survey that included questions about HPV vaccine-related risk perceptions (i.e., perceived efficacy and safety of the vaccine), attitudes toward HPV vaccination, and intentions to vaccinate. Participants in the control group

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did not see any blog and proceeded to complete the survey directly. The entire study took approximately 20 minutes to complete for the treatment groups and about 15 minutes for the control group. The Online Blogs To enhance external validity, we used existing online blogs about the HPV vaccine (located through Google Blog Search) as templates. We selected two blogs with clear opposing views about the vaccine. We ensured that each of the selected blogs was a typical exemplar in its respective category, according to the trends uncovered in previous research (Habel et al., 2009; Kata, 2010; Keelan et al., 2010). That is, the sample blogs were selected to be representative of the sorts of positive and negative content likely to be observed in the blogosphere. Both blogs focused on the effectiveness and safety of the vaccine, with the positive blog indicating that the vaccine is effective and safe and the negative blog suggesting that the vaccine is not effective and is potentially dangerous. We edited the two blogs so they were similar in length and comparable in visual aspects. To increase perceived authenticity of the blogs, we retained the authors’ names, both proven unfamiliar to our study population in a pretest. We also avoided major editorial changes and left the grammatical errors uncorrected. The content of the blogs is shown in Table 1. Key Measures Unless otherwise noted, responses to measurement items were indicated on 1–7 Likert scales with “strongly disagree”

(1) and “strongly agree” (7) as endpoints. Items measuring each construct were averaged to form an index for that variable. HPV vaccine-related risk perceptions. Established scales were adapted to measure HPV vaccine-related risk perceptions (Brabin, Roberts, Farzaneh, & Kitchener, 2006). Perceived vaccine efficacy was measured by the following items: (1) I believe the HPV vaccine is effective in preventing genital HPV; (2) I believe the HPV vaccine works in preventing genital HPV; and (3) I believe if I get the HPV vaccine, I will be less likely to get genital HPV (Cronbach’s α = .89, M = 5.19, SD = 1.23). Higher scores indicate greater perceived vaccine efficacy. Perceived vaccine safety was evaluated through three items: (1) I worry about the short-term side effects of the HPV vaccine; (2) I worry that the HPV vaccine might negatively affect my body; and (3) I worry that the HPV vaccine might have unknown longterm side effects (Cronbach’s α = .86). The final score was reverse coded so higher scores indicate greater perceived safety of the vaccine (M = 2.84, SD = 1.45). Attitudes toward HPV vaccination. Attitudes toward HPV vaccination were assessed by a measure adapted from Abhyankar, Connor, and Lawton (2008). Participants rated “getting the HPV vaccine” on a scale consisting of three 1–7 semantic differential items (bad/good, harmful/beneficial, foolish/wise) (Cronbach’s α = .96, M = 5.62, SD = 1.46). Higher scores indicate more favorable attitudes. Intentions to receive HPV vaccination. Intentions to receive HPV vaccination in the future were assessed in two ways with a scale adapted from previous research (Rothman,

TABLE 1 The Blogs Used as Stimuli in the Experiment The Negative Blog HPV vaccine left teen blind and is ineffective against Cervical Cancer A teenage girl aged sixteen has been left blind after the HPV vaccine according to a report shown be the One Click News group who reported yesterday that a perfectly healthy girl was left almost totally blind, just 10 days after her second HPV vaccine. The report states that initially, there was a visual loss reported in the right eye with a left side headache, however, these symptoms worsened over the next 24 hours to include her left eye with a more severe headache. However, research shows that this is not the only reported case of eye problems following a HPV vaccine. In a paper by Steven M Cohen MD Multiple Evanescent White Dot Syndrome After Vaccination for Human Papilloma Virus and Meningococcus he reports of a case where a 17 year old presented with eye problems after she had the HPV vaccine and Meningococcus vaccine which are two vaccines recommended by the CDC to be given together. It is a pity that those in authority do not, or will not, take this on board. Could this be more to do with the fact that if they dare to acknowledge this important issue then more adverse reactions would be reported and this could be very damaging to both big pharma and governments alike? The Positive Blog The HPV Vaccine—Safe and Effective Protection Against Cancer Cervical cancer is now a preventable gynecological cancer. Two vaccines are available to protect girls and women against the four major types of HPV that cause cervical cancer and genital warts. These vaccines, Gardasil and Cervarix, are inactivated (not a live virus) and expected to be long-lasting and highly effective against the disease. The HPV vaccine is recommended for girls aged 11–12 but can be given to those as young as nine years of age. Ideally the vaccine is given to girls before they become sexually active and exposed to the HPV virus. The vaccine is also recommended for girls and women ages 13–26. The HPV vaccine is administered in a three-dose series, with the second and third doses given two months and six months after the first, respectively. Other vaccines can be given along with the HPV vaccine if for example a child is at an annual pediatrician check-up. In addition, Gardasil is available to boys and men nine through 26 years of age, offering protection against most types of genital warts. Both Gardasil and Cervarix have been extensively studied—21,000 and 30,000 females participated in clinical trials for the vaccines, respectively. There have been few major side effects reported; the most common mild problems include pain, redness, and swelling at the injection site.

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Martino, Bedell, Detweiler, & Salovey, 1999). Participants were first asked to imagine that the HPV vaccine is offered to them free of cost and to respond to the following questions on 1–7 scales anchored by “extremely unlikely” and “extremely likely”: (1) How likely would you be to get the HPV vaccine sometime soon; (2) if you were faced with the decision of whether to get the HPV vaccine today, how likely is it that you would choose to get the vaccine; and (3) how likely would you be to get the HPV vaccine in the future (Cronbach’s α = .95, M = 4.71, SD = 1.87)? Participants were then asked to imagine that they would need to pay $375 (current retail price) for the HPV vaccine and answer the same questions again (Cronbach’s α = .94, M = 2.98, SD = 1.74). Higher scores indicate greater intentions. Participants who had received the vaccine before had the option of choosing “not applicable.” Covariates. A number of variables expected to account for variance in one or more of the dependent variables were also measured so they could be incorporated in later analyses as control variables or covariates. These variables included general attitudes toward vaccination, general beliefs about vaccine efficacy and safety, and HPV-related risk perceptions (i.e., perceived susceptibility to and severity of HPV). General attitudes toward vaccination were measured by a three-item scale (e.g., your general attitude toward vaccination is [very negative/very positive]) (Cronbach’s α = .96, M = 3.97, SD = .83). General beliefs about vaccine efficacy were assessed by a four-item scale (e.g., vaccines are ineffective in presenting diseases) (Cronbach’s α = .85, M = 2.48, SD = 1.15). General beliefs about vaccine safety were gauged by a five-item scale (e.g., vaccination has adverse side effects) (Cronbach’s α = .83, M = 3.14, SD = 1.12). Perceived susceptibility to HPV was measured by a threeitem scale (e.g., it is likely that I will contract genital HPV) (Cronbach’s α = .87, M = 3.23, SD = 1.56). Finally, perceived severity of HPV was assessed by a three-item scale (e.g., I believe that HPV infection has serious negative consequences) (Cronbach’s α = .89, M = 5.60, SD = 1.22). Data Analysis Strategy To answer the research questions, two multivariate analyses of covariance (MANCOVAs) were performed. The first was conducted with the full sample (N = 341). The independent variables (fixed factors) were blog type (negative blog, positive blog, or control) and gender (male vs. female). The covariates included general attitudes toward vaccination, general beliefs about vaccine efficacy and safety, and perceived susceptibility to and severity of HPV. The dependent variables were perceived efficacy and safety of the HPV vaccine, and attitudes toward HPV vaccination. The second MANCOVA was conducted with participants who had never received the HPV vaccine (n = 176). The dependent variables were the two measures of intentions to receive HPV vaccination (free of cost and with cost). The

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independent variables and covariates included in the analysis were identical to those used in the first analysis.

RESULTS Randomization Check A series of chi-squared tests and one-way analyses of variance (ANOVA) were conducted to check the success of random assignment. No significant demographic difference (gender, race, age) was found among the experimental conditions. No significant difference was found with respect to each of the preexisting beliefs or attitudes (general attitudes toward vaccination, general beliefs about vaccine efficacy and safety, and perceived susceptibility to and severity of HPV).2 Main Results The first MANCOVA indicated that, at the multivariate level, both independent variables had significant effects on the dependent variables (blog type: Wilks λ = .898, p < .001; gender: Wilks λ = .946, p = .001). Their interaction was not significant (Wilks λ = .978, p = .503). At the univariate level, blog type had an effect on perceived efficacy of the HPV vaccine that approached significance (F(2, 330) = 2.750, p = .065, η2 p = .016). It had significant effects on perceived vaccine safety (F(2, 330) = 10.773, p < .001, η2 p = .061) and attitudes toward HPV vaccination (F(2, 330) = 12.079, p < .001, η2 p = .068). At the univariate level, gender had a significant effect on attitudes toward HPV vaccination (F(2, 330) = 16.395, p < .001, η2 p = .047). Females, compared to males, held more positive attitudes toward HPV vaccination. Comparisons of adjusted means across experimental conditions (see Table 2 and Figure 1) indicated that the negative blog resulted in significantly lower perceived vaccine efficacy than the positive blog (p = .022). Perceived vaccine efficacy among the control group fell in between, although neither the negative blog (p = .389) nor the positive blog (p = .130) results differed significantly from the control group. Comparisons of adjusted means for the other dependent variables revealed a consistent pattern of results. Compared to the control group, the negative blog significantly decreased perceived vaccine safety (p < .001) and attitudes toward HPV vaccination (p < .001). The positive blog, on the other hand, did not differ in these dependent variables from the control group (both p values >.405). The second MANCOVA indicated that, at the multivariate level, only blog type had significant effects on the dependent variables (Wilks λ = .912, p = .004). Gender effects or the effects of the interaction of gender and blog type were 2 Descriptive statistics for these analyses are available from the first author.

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NAN AND MADDEN TABLE 2 MANCOVA 1: Adjusted Means and Standard Errors

Dependent Variable

Condition

Mean

Perceived vaccine efficacy

Negative blog Positive blog Control Negative blog Positive blog Control Negative blog Positive blog Control

4.981a 5.345b 5.117ab 2.324a 3.085b 3.029b 4.992a 5.802b 5.663b

Perceived vaccine safety

Attitudes toward HPV vaccination

TABLE 3 MANCOVA 2: Adjusted Means and Standard Errors

Std. Error

Dependent Variable

Condition

Mean

Std. Error

0.116 0.107 0.106 0.132 0.122 0.121 0.128 0.117 0.116

Intentions to receive HPV vaccination (free of cost) Intentions to receive HPV vaccination (with cost)

Negative blog Positive blog Control Negative blog Positive blog Control

3.973a 4.872b 4.781b 2.133a 3.103b 3.191b

0.242 0.205 0.214 0.231 0.195 0.204

Note. Means with different superscripts are significantly different from each other at p = .05 level; N = 341.

not significant (gender: Wilks λ = .984, p = .273; interaction: Wilks λ = .970, p = .287). At the univariate level, blog type had significant effects on intentions to receive HPV vaccination free of cost (F(2, 165) = 4.478, p = .013, η2 p = .051) and with cost (F(2, 165) = 6.902, p = .001, η2 p = .077). Comparisons of adjusted means across experimental conditions (see Table 3 and Figure 1) indicated that, compared to the control group, the negative blog significantly reduced intentions to receive HPV vaccination free of cost (p = .014) and with cost (p = .001). The positive blog, on the other hand, did not differ in both intentions from the control group (both p values >.750). A number of significant effects emerged with respect to the covariates. In the first MANCOVA, all covariates, except for general beliefs about vaccine efficacy, had significant effects on the dependent variables at the multivariate level.

Note. Means with different superscripts are significantly different from each other at p = .05 level; N = 176.

In the second MANCOVA, three out of the five covariates (general attitudes toward vaccination, perceived susceptibility to HPV, and perceived severity of HPV) had effects on the dependent variables that were significant or approached significance at the multivariate level. Overall, more favorable beliefs and attitudes toward vaccination in general predicted greater acceptance of the HPV vaccine. Greater perceived susceptibility to and severity of HPV predicted greater acceptance of the HPV vaccine.

DISCUSSION This study sought to determine whether negative and positive blogs about the HPV vaccine had an effect on vaccine-related risk perceptions, attitudes, and behavioral intentions. Previous research has demonstrated the existence of a great deal of vaccine information online, but few studies

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0 Perceived Attitudes toward Intentions to Perceived vaccine efficacy vaccine safety HPV vaccination vaccinate self free of cost –0.2

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Intentions to vaccinate self with cost Negative blog Positive blog

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–1.2 FIGURE 1 Changes in HPV vaccine-related risk perceptions, attitudes, and intentions relative to the control condition.

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have tested the impact of this content on how people think of vaccines. In filling this gap in the literature, we conducted a controlled experiment to test the effects of exposure to antiand pro-HPV vaccine online blogs. Our study clearly showed that participants who read the negative blog post, compared to the control group, perceived the HPV vaccine to be less safe and held more negative attitudes toward HPV vaccination. Exposure to the negative blog also led to lower intentions to receive the vaccine, either with cost or free of cost. These findings demonstrate that even brief exposure to antivaccine information online written by unfamiliar authors can have significant detrimental effects on views toward vaccines. As shown in previous content analyses (e.g., Wolfe et al., 2002; Wolfe & Sharp, 2005), antivaccination websites are commonplace in the online environment. Our findings raise concerns about the possible influence of these websites on the public’s vaccine perceptions. In sharp contrast to the detrimental effects of the negative blog about the HPV vaccine, the positive blog did not significantly alter any vaccine-related risk perceptions, attitudes, or intentions. The asymmetrical impact of positive and negative blogs is intriguing and may be explained by two accounts. First, previous research has shown that negative information, compared to otherwise-equivalent positive information, has a greater psychological impact, a phenomenon known as negativity bias (for a review, see Taylor, 1991). As such, negative information about vaccine efficacy and safety may be inherently more powerful than its positive counterpart. Another explanation may be that participants responded more strongly to the way the negative information is delivered. Rather than presenting summary statistics, the negative blog used individualized stories about dangerous side effects of the HPV vaccine. The positive blog, on the other hand, relied on statistical summaries. Previous studies have found that stories or exemplars are generally more influential than statistical information, possibly due to their greater vividness (for a review, see Taylor & Thompson, 1982). As has been confirmed in previous research (e.g., Kata, 2010), antivaccination information online is often associated with emotional stories about frightening vaccine adverse effects. In contrast to antivaccination content, official information about vaccines, such as the type of information available on the CDC website, is typically presented in statistical summaries and does not evoke fear surrounding vaccinepreventable diseases. Our findings suggest that it may be important for governmental health agencies to reconsider their current message strategies and adopt more personal stories to enhance vaccine communication effectiveness. Our research also sought to examine gender effects on how people respond to negative vs. positive HPV vaccine information online. We did not find such effects. Our analysis did, however, reveal that females held more favorable attitudes toward HPV vaccination than males. Other than gender, HPV vaccine acceptance was also impacted by several additional factors measured within this study.

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Overall, greater acceptance of the HPV vaccine was predicted by more favorable beliefs and attitudes toward vaccination in general, and greater perceived susceptibility to and severity of HPV. Results of this study need to be interpreted within several constraints. First, although the blog posts used as the stimuli for this study were specifically chosen to be typical of online information about the HPV vaccine, our results may not generalize to other online content, such as YouTube videos. Antivaccination or provaccination images may have differing or perhaps greater effects on vaccine perceptions. Second, this study measured message effects immediately after message exposure. The long-term effects of exposure to online blogs about the HPV vaccine are not ascertained. Furthermore, in the real world, Internet users are likely exposed to many sources of HPV vaccine information. What we observed in laboratory studies with a single exposure to one type of information may not be generalizable to the real-world cumulative impact of online information. Future research is also needed to assess the potentially complex effects of conflicting HPV vaccine information originating from different online sources. Third, we did not measure vaccine uptake as a dependent variable. Although risk perceptions, attitudes, and behavioral intentions are good predictors of actual behavior, they are not equivalent to actual behavior. Additionally, although a number of control variables were measured and included in the analyses, other factors potentially associated with HPV vaccine acceptance such as risky sexual behavior and past screening behavior were not included in the analytical models. Finally, our sample was limited to undergraduate students and thus the results may not be applicable to parents who are making the decision to vaccinate their adolescent children. Comprised of college students, the sample was also relatively homogeneous and did not reflect the diversity that exists in the general population. The sample also appeared to have higher than average reported HPV vaccine uptake rates. Future research is needed to replicate this study with a more representative sample. Looking forward, we believe there is a great need for research that systematically documents and explains the effects of exposure to online vaccine information on vaccinerelated perceptions and decision making. Future research may seek to replicate our study with online videos, such as YouTube videos. Although initial analysis of YouTube videos in 2008 (Ache & Wallace, 2008) showed a rather positive portrayal, more recent analysis has revealed a trend toward more negative depiction of the HPV vaccine (Briones et al., in press). Whether and how watching negative YouTube videos about the HPV vaccine might result in negative views toward the vaccine are important research questions to be addressed, particularly given the popularity of YouTube as a video-sharing site. Future research may also examine the impact of anti-HPV vaccine information presented as online news, through social networking sites, and as reports of scientific research. Additionally, future research

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may seek to explore the impact of online information in the contexts of other new and old vaccines, such as those for H1N1, MMR (measles, mumps, rubella), and pertussis. Scholars may also wish to examine the relationship between user-generated messages and offline interpersonal communication regarding vaccination, and ultimately how online interpersonal communication, especially in terms of blogs, and offline interpersonal communication, perhaps the individual’s conversations with medical professionals or other opinion leaders, operate together to affect attitudes, behavioral intentions, and subsequent behaviors (Southwell & Yzer, 2007; Soutwell & Yzer, 2009). Exploratory research on the general features and usage of online blogs as sources for vaccine information may provide additional insights to how such blogs might impact vaccinerelated risk perceptions and decision making. A number of important issues may be addressed. For example, what sociodemographic groups are more likely to be exposed to or seek out such blogs? What psychographic factors are the best predictors of seeking out antivaccination blogs? What content and structural features do these blogs possess and are there differences between anti- and provaccination blogs? What are the profiles of the authors who produce these blogs? Understanding these issues will provide useful directions for future research aimed at assessing blog impact in the area of vaccine risk communication. In conclusion, as people are getting more and more information online, health researchers and professionals need to move beyond simply monitoring information about vaccination and proceed to measure the consequences of this information. This study demonstrates the power of user-generated content in affecting vaccine-related risk perceptions, attitudes, and behavioral intentions. Developing effective strategies for presenting scientific vaccine information and countering misleading, yet powerful, antivaccination information online is critical for maximizing the health-protecting potential of vaccines, especially in the age of Web 2.0.

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