Sexual Orientation Identity Disparities in Awareness and Initiation of the Human Papillomavirus Vaccine Among U.S. Women and Girls

Context The human papillomavirus (HPV) vaccine is effective in reducing the incidence of HPV and cervical cancer and is recommended for all U.S. women and girls aged 11 to 26 years, regardless of sexual identity or behavior. Contribution In a national probability sample, lesbian women and girls, despite being at greater risk for cervical cancer morbidity and mortality, were significantly less likely to initiate HPV vaccination than their heterosexual counterparts. Caution Information was obtained by self-report. Implication Targeted efforts may be needed to increase receipt of the HPV vaccine among U.S. lesbian women and girls. Nearly all cases of cervical cancer are caused by oncogenic strains of human papillomavirus (HPV), and 70% of all cases are linked to types 16 and 18 alone (1). Until the U.S. Food and Drug Administration approved the HPV vaccine for use among women and girls aged 11 to 26 years in 2006 (2), the prevention of cervical cancer centered on regular Papanicolaou (Pap) testing to detect precancerous changes in cervical cells. Today, the HPV vaccine, which targets HPV types 16 and 18, provides an effective strategy for the primary prevention of cervical cancer (3). Lesbian and bisexual women are at risk for HPV and cervical cancer from both female and male sexual partners throughout their life course (46). Indeed, HPV can be transmitted by not only penilevaginal sexual intercourse, in which most lesbians have engaged at some time in their lives (4), but also skin-to-skin or digitalgenital contact with a sexual partner of any sex (610). In addition, the prevalence of genital HPV infection among women with only female sexual partners is similar to that of women who have sex with men (1113). However, despite their risk for HPV infection, lesbians have limited knowledge of female-to-female HPV transmission and its implications for cervical cancer risk and may not perceive prevention messages for HPV and cervical cancer as being relevant to them (1419). The Advisory Committee on Immunization Practices recommends that all U.S. girls and young women aged 11 to 26 years receive the HPV vaccine, regardless of sexual identity or sexual behavior (3). Human papillomavirus vaccination may be especially critical for lesbians, who may be at greater risk for cervical cancer than heterosexual women. At this time, researchers cannot assess cervical cancer incidence by sexual orientation identity because U.S. cancer registries do not collect data on sexual orientation. Nonetheless, several studies have consistently shown that regular Pap testing, which is critical in preventing cervical cancer (20), is lower among lesbians than their heterosexual counterparts (2127). In addition, lesbians may be at greater risk for cervical cancer than heterosexual women because of a higher prevalence of smoking (28), which is a risk factor for cervical cancer (29), and obesity (30), which has been linked to cervical cancer death (31), as well as a lower prevalence of health insurance (21, 3235) and access to health care (34, 36). Despite evidence that lesbians are susceptible to HPV infection and research suggesting that this underserved population may be at elevated risk for cervical cancer morbidity and mortality, no study has investigated the relationship between sexual orientation identity and HPV vaccination among women and girls. Only 1 study has assessed the predictors of HPV vaccination in a national nonprobability sample of predominately white lesbian and bisexual young adult women in the United States (37). Thus, we examined sexual orientation identity disparities in awareness and initiation of the HPV vaccine using a national probability sample of adolescent and young adult U.S women. We hypothesized that lesbians had lower levels of awareness and initiation of the HPV vaccine than heterosexual women and girls and that bisexual and heterosexual women and girls had similar levels of awareness and initiation of the HPV vaccine. Methods Study Participants We analyzed data from the 20062010 National Survey of Family Growth (NSFG), which used a stratified, 3-stage cluster sampling strategy to establish a national probability sample of 12279 civilian noninstitutionalized U.S. women aged 15 to 44 years (38). We restricted our analysis to women aged 15 to 25 years at the time of the survey who participated in year 2 (2007 to 2008), 3 (2008 to 2009), or 4 (2009 to 2010) (n=3253) because older women were not asked about their HPV vaccination history and women who participated in year 1 (2006 to 2007) were not asked about their awareness or receipt of the HPV vaccine. Measures The 2 outcomes of interest were awareness and initiation of the HPV vaccine, and the primary predictor was sexual orientation identity. The 20062010 NSFG assessed awareness by asking, "Before today, have you ever heard of the cervical cancer vaccine, HPV shot, or Gardasil [Merck]? " The survey asked women and girls aged 15 to 25 years who reported having ever heard of the HPV vaccine, "Have you received the cervical cancer vaccine, also known as the HPV shot or Gardasil? " Possible responses for both questions included "yes," "no," or "don't know" (coded as missing). During the Audio Computer-Assisted Self-Interview (ACASI) portion of the survey, respondents were asked about their sexual orientation identity. Response options included "heterosexual or straight;" "bisexual;" and "homosexual, gay, or lesbian," as well as "something else" (in years 1 and 2 only), "don't know," or "refused," which were grouped into a single "not reported" category. The choice of covariates included in statistical models was informed by ecosocial theory, which emphasizes the embodiment of societal factors in the form of population health outcomes, including health inequities (3943). Prehypothesized covariates, shown with their categorization in Table 1, included sociodemographic factors and indicators of health care access and utilization. Table 1. Distribution of Sociodemographic Factors and Health Care Indicators Among U.S. Women and Girls Aged 1525 y, by Sexual Orientation Identity Statistical Analysis After generating descriptive statistics for all prehypothesized covariates by sexual orientation identity, we used multivariable logistic regression models, which included sociodemographic factors and indicators of health care access and utilization to obtain adjusted prevalence estimates (predictive margins) of awareness and initiation of the HPV vaccine among U.S. women and girls aged 15 to 25 years for each sexual orientation identity group. Predictive margins use the distribution of covariates in the study population to obtain standardized outcome estimates that can be compared across groups (44, 45). The predictive margin for a given sexual orientation identity group represents the average predicted response if everyone in the study population had been a member of that group (44, 45). The P values for the comparison of awareness and initiation of the HPV vaccine between a given sexual orientation identity group and heterosexual women and girls (reference group) were obtained from the underlying multivariable logistic regression models (44). All analyses accounted for the complex survey design (stratification; clustering; and sampling, response, and coverage rates) using the svy commands in Stata, version 13 (StataCorp). We determined that our sample was large enough on the basis of our estimation that 43 lesbians and 43 heterosexual women and girls would provide 80% power to detect expected differences in HPV vaccination, assuming prevalence estimates of 10% among lesbians and 34.5% (46) among heterosexual women and girls and a type I error of 0.05. No data were missing for awareness of the HPV vaccine; among women who had ever heard of the HPV vaccine, 6 (0.23%) were missing data on initiation. Missing data for age, race/ethnicity, religion in which the respondent was raised, relationship status, education level, household poverty level, employment status, and health insurance status were imputed by NSFG staff using the sequential regression imputation method (47). The proportion of women and girls missing data on covariates that were not imputed by NSFG staff was small (0.3%). This study was not determined to be human subject research by the Office of Human Research Administration at Harvard Longwood Medical Area (Boston, Massachusetts). Role of the Funding Source This study was funded by the National Cancer Institute. The funding source played no role in the design or conduct of the analyses, the interpretation of the results, or the decision to submit the manuscript for publication. Results Using 20062010 NSFG data (the response rate for the entire sample for women aged 15 to 44 years was 77.7%; the response rate for women aged 15 to 19 years and 20 to 44 years was 77.4% and 77.7%, respectively), we estimated the distribution of sociodemographic factors and indicators of health care access and utilization by sexual orientation identity among U.S. adolescent and young adult women (Table 1). Among women and girls aged 15 to 25 years (n=3253), lesbian respondents tended to be older and have been raised in a nonreligious household relative to their heterosexual counterparts. Although lesbians were more likely to work in the labor force, have a high school degree or higher, and have a household income at or above 200% of the federal poverty level than heterosexual women and girls, they were more likely to be uninsured or underinsured and were considerably less likely to have received contraception and sexually transmitted infection (STI) services in the past year. Bisexual women and girls were more likely to be white, have been raised in a nonreligious household, and be living below 100% of the federal poverty level than their heterosexual counterparts; they were also less likely to be working in the labor force and have a bachelor's degree or higher. In addition, bisexual