Our analysis of a nationally representative survey finds limited HPV vaccine initiation among young adult women in the United States. Previous national estimates reported that 10–11% of 18 to 26 year old women had received at least one dose of the vaccine by the end of 2007. 28, 31
We estimate that, in 2008, 12% of this age group received the vaccine. This minimal increase in vaccine uptake among young adult women stands in contrast to coverage among adolescents ages 13 to 17, which increased substantially, from 25% in 2007 to 37% in 2008 and to 44% in 2009, according to estimates from the National Immunization Survey-Teen.32–34
Higher vaccine coverage among adolescents than among young adults may be due, in part, to differences in recommendations regarding adult vaccination. A previous study identified provider recommendation as a driving factor in HPV vaccination among 19 to 26 year old women.35
In keeping with American Cancer Society guidelines, some clinicians may be consulting with patients on a case by case basis to determine if HPV vaccination is likely to be beneficial. In addition, public financing of vaccines for uninsured and under-insured minors through the Vaccines for Children program may be helping to boost overall HPV vaccination rates among adolescents, and to reduce disparities in vaccine coverage by insurance, income and race or ethnicity in this age group.33
Most federal and state vaccine financing programs do not extend to adult women, unless they initiate the HPV vaccine series before turning age 19.36
Thus, in the vaccine’s initial two years on the market, it is not surprising to observe that young adult women exhibit lower overall vaccination rates than adolescents, and that uninsured young adult women are significantly less likely than privately or publicly insured young women to receive the vaccine. Uninsured women are at high risk for poor cervical cancer screening participation,37
and consequently, for cervical cancer morbidity and mortality.38
Uninsured women would, therefore, greatly benefit from catch-up HPV vaccination, especially if they have not initiated sexual activity. Discretionary use of Section 317 funds to pay for HPV vaccines for uninsured adults, Merck’s Vaccine Patient Assistance Program, and state-level efforts to bundle free HPV vaccination with cervical cancer screening services, may help to expand vaccine coverage among uninsured young adult women.36, 39
Such efforts may be particularly important given that the majority of women interested in receiving the HPV vaccine are not willing to pay full price, but would be willing to obtain the vaccine free or at much lower cost.
Although HPV vaccine initiation is higher among adolescents than among adults, 2008 NHIS data indicate that the dose completion rate is higher among adults than among adolescent girls (58% versus 41%).40
This high completion rate among young adults may be reflective of the higher motivation of women who seek and complete the vaccine series of their own volition, rather than due to prompts from parents or school-based programs. Examination of the drivers and barriers to vaccine completion is a priority for future research, as vaccine efficacy is unknown for receipt of fewer than three doses.6
We found preliminary evidence that unmarried women – that is, women with a higher risk of future HPV infection through sexual contact with new partners – were much more likely to be vaccinated than married women, despite the fact that married and unmarried young adult women were equally likely to have heard of the HPV vaccine. This finding suggests that some young adult women or health care providers may be appropriately assessing future risk of HPV infection, and the potential benefits from HPV vaccination.
Nearly half of respondents who were not interested in the HPV vaccine reported that their lack of interest was because they did not need the vaccine, or were not sexually active. In the absence of information on the sexual history of respondents, these results must be interpreted with caution. It is possible that women who are in long-term, monogamous relationships, or those who are not planning to become sexually active in the foreseeable future, are making accurate assessments of their low future risk of HPV infection, and therefore, their limited potential benefits from HPV vaccination. Alternatively, however, these stated reasons for lack of interest in the HPV vaccine may indicate that women who have not yet initiated sexual activity do not know that the HPV vaccine is more efficacious if administered before they become sexually active. If this latter scenario is the case, then public education targeted to this age group regarding the benefits of HPV vaccination is warranted.
Although recent cervical cancer screening participation was associated with awareness of the HPV vaccine, neither recent nor ever screening was correlated with likelihood of HPV vaccination. As the majority of women in our study had been screened recently, or were younger than the age at which clinical guidelines definitively recommend cervical cancer screening initiation, we may not have been able to detect differences between screened and unscreened subgroups of women. However, we did find evidence that women’s other vaccination behavior was associated with receipt of the HPV vaccine. Consistent with previous studies, we found that those who had received a flu shot in the past year, or had received one or more recommended lifetime vaccines (Hepatitis A or B, and/or tetanus), were substantially more likely than those who had not to receive the HPV vaccine.28–29
Our study has a number of limitations. First, unlike the National Immunization Survey, self-reported NHIS data are not validated against provider immunization records. Consequently, there may be response biases; however, given how new and widely discussed the HPV vaccine is, it seems likely that respondents would remember and report their HPV vaccine status accurately. Second, NHIS 2008 did not collect data on sexual history, which limited our ability to evaluate whether HPV vaccines reached subgroups of women likely to benefit from vaccination. NHIS could be used to examine this issue if questions on age of sexual initiation and timing of vaccine dose administration were included in future rounds of data collection.
Third, as NHIS 2008 data were collected within two years of the introduction of HPV vaccine, older members of the cohort under study never had the opportunity to vaccinate as adolescents. Therefore, we do not expect our results to generalize to the HPV vaccination behavior of future groups of young adult women. Future research should monitor whether the patterns of use we observe continue as the vaccine has been on the market for a more extended period. In addition, as data become available, vaccine dose completion rates should be examined to identify factors that promote and/or impede completion. Current estimates of dose completion likely underestimate true completion rates, as insufficient time has elapsed for many of the respondents to have received second and third doses of the vaccine.
HPV vaccine coverage among young adult women was low in 2008, and was largely driven by high rates of vaccination among 18 to 20 year olds, who may have been vaccinated as minors. Catch-up was higher among insured than uninsured young adult women. As uninsured women are at greater risk of cervical cancer morbidity and mortality, they should be a high priority for catch-up vaccination. Coordinated public vaccine financing programs like Vaccines for Children seem to be effective at promoting vaccine coverage among uninsured adolescents, and may have potential for expanding catch-up vaccination among young adult women who stand to benefit the most from HPV vaccines.