Human papillomavirus (HPV) and related diseases are major public health problems in the United States. Approximately 20 million Americans are currently infected with HPV while another 6 million are newly infected each year [1
]. In 2010, an estimated 12,200 new cases of invasive cervical cancer - the most severe consequence of HPV infection - were diagnosed, and 4,210 women died from cervical cancer [2
]. Over the past decades, a steady decrease in the cervical cancer incidence and mortality has been reported [2
]. Still, cervical cancer disproportionately affects poor minority women [3
]; along with increased incidence of cervical cancer among female population groups with lower education and income, and higher poverty [4
], substantial disparities in stage at diagnosis and mortality also remain by race/ethnicity [3
The persistent, albeit, diminishing socioeconomic disparities in overall cervical cancer incidence and mortality, can be partly explained by the constantly lower screening rates among disadvantaged populations, despite the widespread acceptance of the Papanicolau (Pap) test [9
]. The recent Food and Drug Authority (FDA) approval of HPV vaccines which prevent the most common HPV infections (Gardasil®
in 2006 and Cervarix®
in 2009) [13
] has provided an additional opportunity to reduce the burden of cervical cancer. This medical breakthrough can also potentially reduce cervical cancer disparities since high-risk groups [3
] are the ones expected to benefit the most from HPV vaccines. Yet, these high-risk groups are less likely to receive the Pap test [11
]. Although HPV vaccines are widely regarded as a key preventive measure for the universal benefit of all women [15
], early evidence of lower HPV vaccination rates among poor minority women [16
] indicates that disparities persist even in HPV vaccination. It is therefore critical to better understand the underlying factors of the disparities in HPV vaccination to maximize the HPV vaccines' potential for reducing the racial/ethnic and socioeconomic disparities in cervical cancer.
Major barriers to HPV vaccine implementation among at-risk populations include high vaccination costs and lack of a usual source of care. Limited community involvement in stimulating awareness of cervical cancer and available screening methods is another important obstacle that needs to be overcome [15
]. Awareness is usually the first stage in the process of adopting a particular preventive health behavior [19
]. Previous studies from the US and the UK have found that racial/ethnic minorities and socioeconomic disadvantages were associated with lower levels of awareness of either HPV vaccination or HPV [16
]. Acceptability of the HPV vaccine, however, was not necessarily lower among racial/ethnic minorities and socioeconomically disadvantaged groups in the US [22
]. Among a multi-ethnic sample of 18-to-55-year-old women in Los Angeles County, California, Latinas and Asian/Pacific Islander women were more willing to be vaccinated than White or Black women, whereas education was inversely associated with the intention to become vaccinated [22
]. Interestingly, the highest levels of HPV vaccine acceptability were reported among the least educated and poorest individuals, although most of the estimated differences by racial/ethnic and socioeconomic characteristics were statistically insignificant at the 5% significance level [26
]. A systematic review on HPV vaccine acceptability also found that lower education levels were associated with higher acceptability and that racial/ethnic minority groups showed similar levels of acceptability [25
]. These findings suggest that racial/ethnic minorities and socioeconomically disadvantaged population groups who are less likely to be aware of the HPV vaccine, can potentially show even higher levels of HPV vaccine acceptability if they were given adequate information. If true, this hypothesis has important implications for public health practice and prevention policy. It can offer another rationale for public health programs to further raise HPV vaccine awareness among racial/ethnic minorities and socioeconomically disadvantaged groups, and strengthen policy efforts to address other barriers to HPV vaccination.
Little attention, however, has been paid to the potential impact of improving HPV vaccine awareness on increasing HPV vaccine acceptability at a population level. Observed differences in HPV vaccine acceptability levels between the previously "aware" and "non-aware" groups, including results from standard regression models, can be misleading because the two groups may differ in many unobserved ways. If the aware group consists of more advantaged individuals who may be more (less) acceptable of vaccinations, a fair comparison in HPV vaccine acceptability between the aware and non-aware groups cannot be achieved because the difference in acceptability may overestimate (underestimate) the marginal effect of improved HPV vaccine awareness.
This study aimed to quantify the marginal effectiveness of increasing HPV vaccine awareness on acceptability, using a nationally representative sample of women who reported having any female children under the age of 18 in the household. The hypothesis to be tested is that HPV vaccine awareness increases vaccine acceptability and that this population-level estimate is greater when unobserved heterogeneity between the aware and non-aware groups is taken into account than otherwise. To this end, the current study exploited a unique survey question that captured hypothetical HPV vaccine acceptability, and employed a statistical method that controlled for unobserved differences between the two comparison groups.