The human papillomavirus (HPV) vaccine is expected to significantly reduce HPV-associated diseases such as cervical cancer, anal cancer, and genital warts. Despite this potential, less than half of females aged 13 to 17 years had received any doses of the HPV vaccine as of 2010.1 These low immunization rates persist despite increasing awareness that HPV is the most common sexually transmitted virus in the United States2,3 and that adolescents and young adults are at highest risk of contracting this infection.4
Vaccinating adolescents against HPV requires parental consent, and thus, acceptability of the vaccine among parents is critical for improving its uptake. Studies have previously shown that parental beliefs and attitudes toward vaccination are important predictors of vaccination intention.5–9 The Health Belief Model categorizes these vaccine-specific beliefs into key predictors of vaccine acceptability, including perceived disease likelihood and severity, vaccine benefits, and barriers to vaccination.10,11 Therefore, better understanding of parental beliefs toward the HPV vaccine and how these translate into health behavior is critical for developing interventions designed to improve adolescent HPV vaccine uptake.
Many studies have examined the attitudes and beliefs of US parents related to HPV vaccination intention,6,9,11–16 yet standardized tools to assess parental views of this vaccine are not widely available. A notable exception is the Carolina HPV Immunization Attitudes and Beliefs Scale (CHIAS) developed by McRee et al.17 This scale, based on constructs from the Health Belief Model,10 was tested in a population of caregivers of adolescent females living in areas of North Carolina with high cervical cancer rates. After rigorous psychometric and validity testing, analysis of the CHIAS identified 4 factors that were reliably associated with HPV vaccination intention among this population—harms, effectiveness, barriers, and uncertainty. In a subsequent longitudinal assessment of the CHIAS, the barriers construct was found to reliably predict actual HPV vaccine uptake by adolescent daughters of these parents over a 1-year time frame.18
Having a standardized measure of parental attitudes and beliefs that are predictive of HPV vaccination would be a significant advance in the development and implementation of comprehensive interventions to increase HPV vaccination rates. Although the CHIAS provides an excellent foundation, it is unclear whether it is applicable to the broader US population. To address this, we tested a modified version of the CHIAS among a national population of mothers of adolescent females. The goals of this study were to determine: (1) whether applying the CHIAS to a national sample of mothers resulted in similar “groupings” of factors (harms, effectiveness, barriers, and uncertainty) as identified in the original study and (2) whether the associations between the identified attitudinal constructs and maternal HPV vaccination intention in a nationally representative population were similar to that of the original CHIAS study population.
Our survey was implemented from August 13 to September 7, 2010, as part of the C. S. Mott Children's Hospital National Poll on Children's Health (NPCH)—a recurring, nationally representative survey of adults with and without children in their homes. The focus of this article is on responses to CHIAS- and HPV-related items that were administered specifically to the subsample of female respondents who indicated that they were the parent, step-parent, or guardian (henceforth defined as “mothers”) of a female child between the ages of 11 and 17 years. The study was approved by the University of Michigan Medical School's Institutional Review Board. Survey questions are available on request.
The NPCH survey is conducted using the web-enabled KnowledgePanel, a probability-based panel designed to be representative of the US population. Initially, participants are chosen scientifically by a random selection of telephone numbers and residential addresses. Persons in selected households are then invited by telephone or mail to participate in the web-enabled KnowledgePanel. For those who agree to participate but do not already have Internet access, Knowledge Networks provides at no cost a laptop and Internet service connection. Others who already have computer and Internet service are permitted to participate by using their own equipment. Panelists then receive unique log-in information for accessing surveys online and are sent e-mails throughout each month inviting them to participate in research. Knowledge Network's KnowledgePanel has served as the sampling frame for several other peer-reviewed studies on health topics related to children.19–23
Our analyses specifically included the 228 female respondents self-identified as mothers of adolescent females. These respondents were administered the CHIAS- and HPV-related questionnaire regardless of whether their daughter had received any doses of the HPV vaccine. Mothers with >1 adolescent daughter were asked to respond with regard to their youngest adolescent girl. This sample of mothers was derived from a larger sample of 2184 households (including parents and nonparents) that were recruited for participation in the entire NPCH, which contained questions about a variety of health issues. Our study was restricted to mothers to be consistent with the original CHIAS study, in which 94% of respondents were female caregivers. Before the survey, all respondents were provided with a brief paragraph about HPV and HPV vaccines: “Human papillomaviruses (also known as HPV) can cause cervical cancer and genital warts in women. A vaccine against the most common types of HPV is available for adolescent girls and young women. Three shots of the vaccine are needed to be fully protected from getting HPV.”
We used previously published studies of the CHIAS17,18 and of important parental attitudes regarding the HPV vaccine9,12,13 to derive a series of 14 questions related to attitudes and beliefs about HPV infection and the HPV vaccine. Because of space constraints, some of the original 18-item CHIAS measures were deleted or modified. A comparison of the original CHIAS items and the modified scale is shown in the Appendix Table A2 (online only, Supplemental digital content, available at: http://links.lww.com/OLQ/A34). Responses were graded using a 4-point response scale (“strongly disagree,” “disagree,” “agree,” and “strongly agree”) and were coded such that higher values indicated stronger agreement with the statement and corresponded to less support for vaccines. Three of the 14 items were reverse coded so that higher values would similarly correspond to less support for vaccines.
The primary outcome assessed was HPV vaccine uptake, in which mothers were dichotomized as having daughters who did or did not receive any HPV vaccine doses. Vaccination intention was assessed as a secondary outcome measure because: (1) a majority of our study population included mothers who had not vaccinated their daughters against HPV; and (2) this was consistent with the original CHIAS study, which examined associations between factor groupings and vaccination intention (defined as those responding “probably” or “definitely” to the question of whether they would have their daughter vaccinated against HPV in the next year). In our study, we assessed vaccination intention among mothers of unvaccinated girls in 2 ways. In the first, which was the manner most consistent with the original CHIAS, we assessed agreement with the statement “I intend to get my daughter vaccinated against HPV in the next 6 months,” using a 5-point response scale. Results were later dichotomized into positive intentions or not (“agree/strongly agree” vs. “neutral/disagree/strongly disagree”). In the second, vaccination intention was measured by assessing agreement with the statement “I will never get my daughter vaccinated against HPV.” This outcome, termed “ever intend to vaccinate” was defined by the responses “disagree” or “strongly disagree” to the statement whereas “never intend to vaccinate” included the responses “neutral,” “agree,” or “strongly agree.” All 3 outcome measures (did/did not receive the vaccine, vaccination in next 6 months, and ever/never vaccinate) were assessed for associations with factor groups identified in our study.
Other Predictor Variables
Demographic characteristics including mother's age, race/ethnicity, education, household income, area of residence, and daughter's age were provided by the survey vendor. Census-based probability sampling weights provided by the survey vendor were applied to the analysis to allow nationally representative estimates to be derived. For our analyses, demographic variables were categorized as in the CHIAS study to compare study populations.17 Race/ethnicity was provided by the survey vendor as 5 mutually exclusive categories (non-Hispanic white, non-Hispanic black, non-Hispanic other, 2+ races, or Hispanic). The categories “non-Hispanic other,” “2+ races,” and “Hispanic” were combined into one category “Hispanic or other” because of low sample sizes in these categories. Education was dichotomized as high school or less versus some college or greater, and household income was dichotomized as less than $50,000 versus greater than or equal to $50,000 to improve statistical power. Area of residence was provided by the survey vendor as “metropolitan area” or “nonmetropolitan area”, whereas in the CHIAS study, this was defined as rural or urban residence using the United States Census classification.
An exploratory factor analysis of the modified CHIAS was conducted using principal components analysis with oblique rotation method (as factors were assumed to be correlated). Factors meeting the Kaiser criterion (eigenvalues ≥1.0) were retained. Three items were reverse-coded such that higher values consistently corresponded to less support for vaccines, and the factor analysis was rerun to facilitate subsequent analyses. Factor scores were created for each respondent by calculating the mean of the responses to all items loading onto each factor. Factor scores were also determined using regression scoring methods, which assigned weights to individual items in the derivation of factor scores. Results between the weighted and nonweighted methods were similar; thus, we present only nonweighted factor scores in this article so as to be consistent with the original CHIAS study. Cronbach's α coefficient was used to evaluate the internal reliability of each factor grouping.
Logistic regression analyses assessed bivariate associations between HPV vaccination intention (measured as 3 different outcomes) and covariates of interest, including weighted demographic characteristics and nonweighted factor scores. Multivariate analyses examined the relationship between the outcome measures (HPV vaccine uptake and vaccination intention) and all of the identified factors, which were hypothesized a priori to be important predictors. Given that none of the demographics had significant associations with HPV vaccination intention in bivariate analyses, these were not included in the final multivariate models. P values ≤0.05 were considered statistically significant. All analyses were performed using STATA 10.0 (StataCorp, College Station, TX, 2007). Probability sampling weights provided by the survey vendor were applied to the sample to derive nationally representative estimates.
The overall survey participation rate among parents was 57% (n = 1621 parents with children <18 years of age in the household). There were 442 households that had at least one female child aged 11 to 17 years. Questions regarding HPV vaccination beliefs and attitudes (i.e., the modified CHIAS) were administered only to female respondents (“mothers”), resulting in 228 respondents. Among these mothers, 39.5% (n = 90) reported that their daughter had received at least 1 dose of the HPV vaccine. Of these, nearly 75% (n = 67) reported that their daughter had completed the 3-dose series. Weighted demographics of mothers whose daughters had not received any vaccine doses are shown in Table 1.
The initial exploratory factor analysis used the entire sample of mothers (regardless of daughters' HPV vaccination status). Three factors were identified as conceptually meaningful and could describe the variation among responses. There was strong correlation among the items in each factor grouping, as shown by the Cronbach's α coefficients (Table 2).
Results were largely consistent with the findings from the original CHIAS study. The first factor identified, which we labeled “harms/ineffectiveness,” contained 9 items and included statements assessing for perceived harms from vaccination such as short- or long-term health problems and lack of sufficient safety data (Table 2). Also loading onto this factor were 2 statements regarding the potential lack of vaccine benefit including the vaccine's ineffectiveness in preventing cervical cancer and the belief that vaccination is unnecessary because of the availability of cervical cancer screening. A notable difference between our results and that of the CHIAS is that harms and effectiveness loaded as distinctly separate factors in the original CHIAS.
As in the CHIAS study, the second factor identified in our study, “barriers,” contained 3 highly correlated items that addressed potential barriers to HPV vaccination, including access to affordable and convenient vaccination opportunities (Table 2).
In both the modified scale and CHIAS, items concerning doctors' or peers' attitudes about vaccines loaded onto a third factor, which we called “social norms” (Table 2). Although in the original CHIAS study other items concerning lack of sufficient vaccine information also loaded onto this factor (which was called “uncertainty”), some of those items were not included in the modified scale.
To be consistent with the original CHIAS study, we repeated the exploratory factor analysis specifically among the subpopulation of mothers whose daughters had not received any HPV vaccine doses. The same 3 groupings of factors, “harms/ineffectiveness,” “barriers,” and “social norms,” were identified. However, in this subset analysis, 1 item was dropped (“The HPV vaccine is so new that I want to wait a while before deciding if my daughter should get it.”) because of low factor loadings. Among this subpopulation, the mean factor scores for perceived harms (2.54, SD 0.63), barriers (1.91, SD 0.66), and social norms (2.57, SD 0.70) were similar to what was found for the entire sample (Table 2).
Associations With Vaccination
We performed bivariate and multivariate analyses examining associations between the factors and actual HPV vaccine uptake (did/did not receive the vaccine). All 3 factors were significantly associated with HPV vaccine uptake in bivariate analyses. However, in the multivariate model, only harms/ineffectiveness and social norms remained associated with vaccine uptake. Respondents with a higher level of perceived harms had a lower likelihood of having had their daughters receive the HPV vaccine, with an odds ratio (OR) of 0.16 (95% confidence interval: 0.07, 0.34), as did mothers who reported lower influence from perceived social norms (OR: 0.48, 95% CI: 0.26, 0.88).
Associations With Intentions to Vaccinate
The original CHIAS study assessed vaccination intention by measuring agreement with “intention to vaccinate in the next year,” and all 4 factors identified (harms, barriers, effectiveness, and uncertainty) were found to be associated with this outcome in multivariate models. Using “likelihood of vaccination in the next 6 months” as the measure of vaccination intention in our study, the factors harms/ineffectiveness and barriers were significantly associated with intention to vaccinate in both bivariate and multivariate analyses. There was 90% lower odds of positive vaccination intention for every 1-point increase in the factor score for harms/ineffectiveness, and over a 3-fold increased odds of intention to vaccinate for every 1-point increase in the barriers' factor score in the multivariate model (Table 3).
When bivariate analyses were repeated using the broader measure of vaccination intention (ever/never intend to vaccinate), all 3 factor groupings were significantly associated with vaccination intention (Table 3). However, in the multivariate model, only harms/ineffectiveness remained significantly associated with intention to vaccinate.
The CHIAS scale is a rigorous measure of parental attitudes and intention for HPV vaccination that was shown to predict adolescent HPV vaccine uptake longitudinally when tested among a sample of parents, mostly mothers, from North Carolina. When we applied a modified version of the CHIAS scale to a national sample of mothers of adolescents, we identified a similar, although more compact, factor structure underlying HPV vaccine attitudes and beliefs. The consistency between the 2 studies suggests that the factors harms/ineffectiveness, barriers, and social norms are important attitudinal constructs that can be validly applied across the US population of mothers. As in the original CHIAS study, our cross-sectional analyses also demonstrated that harms/ineffectiveness and social norms were independently associated with actual HPV vaccine uptake in multivariate models.
There were 2 main differences in the factor profiles between our study and that of the CHIAS. The first is that, in the CHIAS study, harms and effectiveness were separately identified as 2 factors, whereas in our study statements related to harms and effectiveness loaded onto a single factor (“harms/ineffectiveness”). One possible hypothesis for this difference could be that in our population, mothers who reported increased concerns about vaccine safety also perceived less potential benefit from the HPV vaccine. This suggests that beliefs about vaccine safety and effectiveness may align together in a parent's mind and additively affect vaccination decisions. Alternatively, these differences could be because of variation between our study population and that of CHIAS (see Appendix Table A1 [online only, Supplemental digital content, available at: http://links.lww.com/OLQ/A34] for population comparison). For example, we focused exclusively on mothers, and our study had a higher proportion of less-educated individuals who have been shown in some studies to be more likely to intend to or have their daughters vaccinated than mothers who have received higher education.24–26 Compared with the CHIAS study, our sample also included more mothers belonging to Hispanic or other ethnic groups, which have been shown to associate HPV vaccine acceptability with both safety concerns and beliefs about vaccine protection against cervical cancer.8,27
The second difference between our results and that of the CHIAS study was that we did not find “uncertainty about the vaccine” to be a factor in our study population. This could be because of differences in the statements used in the modified compared with the original CHIAS (Appendix Table A2 [online only, Supplemental digital content, available at: http://links.lww.com/OLQ/A34]). Specifically, the original CHIAS' uncertainty factor included the item “I don't have enough information about the HPV vaccine to decide whether to give it to [child's name],” which was not asked in our study. In addition, the CHIAS study was conducted shortly after the introduction of the vaccine, when uncertainty was likely to be higher than the more recent timing of our study.
The CHIAS “uncertainty” factor, however, does overlap with the factor “social norms” identified in our study, as both included the item “Other parents in my community are getting their daughters the HPV vaccine.” Further supporting the idea that “uncertainty” and “norms” may be assessing similar concepts is the fact that both factors were associated with HPV vaccination intention in bivariate analyses in their respective studies. Our findings suggest that mothers who believe that their peers in the community or their children's doctors support the HPV vaccine are more likely to have positive HPV vaccination intentions.5 Thus, as shown previously,9,24,28 doctors can help significantly promote HPV vaccination by routinely conveying their vaccine recommendations to parents.
As with the original CHIAS study, barriers played a relatively small role in HPV vaccination intention overall and actually had a “positive” association with intention to vaccinate in the next 6 months. These somewhat counterintuitive results support the hypothesis that mothers with an active intention to vaccinate in the near future may have done more research and acquired greater awareness of potential barriers to vaccination. It also suggests that barriers to vaccination and awareness of these potential challenges do not appear to sufficiently influence mothers' vaccination intentions in a negative fashion. As discussed by Gerend et al,29 barriers are likely multidimensional, and the barriers included in the modified CHIAS may capture only one dimension—that is, the practical concerns raised by parents who are considering vaccination. These practical barriers may be salient only for parents considering vaccination and do not include global barriers that are relevant for individuals not intending to vaccinate; as a result, practical barriers are likely to be positively related to intentions,29 as we saw in our study. Taken together, these data suggest that future interventions should focus on providing solutions to practical barriers to HPV vaccination in current health systems, which may enable mothers who intend to vaccinate their children to actually succeed in doing so.
As this was a cross-sectional study, causal inferences cannot be made about the associations between HPV attitudes/intentions and vaccine uptake. Future research using a national sample is needed to explore whether the factors associated with HPV vaccination intention identified in the CHIAS, and confirmed in our study, predict actual HPV vaccine uptake over time. Brewer et al (2011) performed a longitudinal study that assessed the predictive properties of the CHIAS for actual adolescent HPV vaccine uptake in a population living in North Carolina and found that only “barriers” predicted actual vaccine initiation at 1-year follow-up.18 This was an unexpected finding because barriers had not been found to be as important as other factors in the original cross-sectional analysis that examined vaccination intention. Although it will be important to assess which of the constructs identified in our study predict vaccine uptake nationally, the similarities between our cross-sectional results and that of original CHIAS study (which was also cross-sectional) suggest that the longitudinal findings of Brewer et al may also be applicable across the broader US population. If so, such findings would have important implications for the development of public health interventions targeting HPV vaccination as it would suggest that barriers are the most important issue to be addressed.
A strength of this study is that it focused on a nationally representative US population, which increases the potential generalizability of our findings. Our study population reported similar rates of adolescent HPV vaccine uptake as national estimates, with roughly 4 in 10 adolescent females receiving at least 1 HPV vaccine dose.1 In addition, we included both mothers who had and had not vaccinated their daughters to explore how HPV attitudes and beliefs are associated with negative and positive vaccination intentions/action. The similarities of results across our different analyses and to the CHIAS study highlight the robustness of the CHIAS as a valuable tool for assessing maternal attitudes about HPV vaccination in a standardized manner.
Our results should be interpreted in light of some limitations. As with any survey, participation bias could have affected our results. Our survey was web-based and delivered to a panel of participants who indicated a general interest in survey participation and thus may have differences in health beliefs from the nonsampled population. Participation bias is minimized by the fact that participants were not aware of the health topics included in the survey before agreeing to participate. Additionally, it is possible that responses to CHIAS items reflect knowledge/awareness about HPV rather than attitudes and beliefs because our study did not specifically include items assessing respondents' HPV knowledge due to space constraints. However, this is likely minimized by the fact that the study was conducted at least 4 years after FDA licensure of the quadrivalent HPV vaccine for females30 and that a high proportion (40%) of respondents had started the HPV vaccine series for their daughters, indicating familiarity with the vaccine. Furthermore, although our study population was relatively small (n = 228), the reproducibility of our results across different analytic approaches and outcome measures as well as the strong correlations with findings from the original CHIAS study strengthen the validity of the results. Future studies will need to examine specifically whether the CHIAS predicts HPV vaccination among adolescents nationally.
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