Human Papillomavirus Vaccination Series Initiation and Completion, 2008–2009

DISCUSSION

To our knowledge, this is the first study to examine national data on HPV vaccination initiation and completion among adolescent girls by using provider-verified vaccination records. Approximately 40% of girls received ≥1 HPV vaccine dose and, of those girls, approximately one-half completed the 3-dose vaccination series. Although some factors were associated with both vaccination series initiation and completion, there were differences. Race/ethnicity was not associated with initiation; however, black and Hispanic adolescents were less likely to complete the series, compared with white adolescents. Daughters of younger mothers were more likely to initiate the series, whereas daughters of older mothers were more likely to complete it. Although access to vaccine is provided for uninsured girls through the VFC program, the lack of a medical home might contribute to lower coverage rates among VFC-eligible, uninsured girls and girls who received all of their vaccines at public facilities. The most common reason for nonintent to vaccinate one's daughter against HPV was lack of knowledge about the vaccine. These data provide information that could help identify ways to increase HPV vaccine coverage in the United States.

One of the factors most strongly associated with HPV vaccination initiation was receipt of a provider recommendation. Previous studies showed that provider recommendations influence parental decisions to receive HPV and other vaccinations.^7,–,10 Various barriers at the provider level lead to missed opportunities for vaccination, including vaccine costs, insurance coverage, discomfort discussing sexuality, and a preference to vaccinate older adolescents.^11,12 To address cost and reimbursement barriers, the National Vaccine Advisory Committee recommended improving business practices to ensure vaccine reimbursement, participating in vaccine-purchasing pools, and improving reimbursement through the VFC program.^13,14 Similar to previous studies, we found that older adolescents were most likely to have initiated HPV vaccination.^15,–,17 Although HPV vaccination is recommended for girls at 11 or 12 years of age, pediatricians and family medicine physicians are more likely to recommend HPV vaccination strongly for older adolescents.¹² Strong provider recommendations for HPV vaccination likely would improve vaccine uptake at the recommended age.⁸ Limited health care access might hinder receipt of a provider recommendation. In the model without inclusion of provider recommendation, a few additional variables reflecting access to care became significant. Therefore, increasing access to health care, removing provider barriers, and encouraging stronger provider recommendations all could increase vaccine uptake.

Higher coverage rates among older adolescent girls might reflect more opportunities for catch-up vaccination as adolescents grow older. The adolescent platform promotes an 11- to 12-year preventive health check for vaccination and health screening.^18,–,20 We found that girls who underwent an 11- to 12-year preventive check were more likely to have initiated vaccination than were those without such a visit. However, there was no difference in coverage rates among girls who underwent an 11- to 12-year preventive check and those who were >12 years of age at the time of vaccine licensure, which indicates that older adolescents were being vaccinated during subsequent health care encounters. Approximately 50% of girls were >12 years of age at the time of HPV vaccine licensure, and the 2009 NIS-Teen 1996 birth cohort is the first full cohort that can be assessed for receipt of the HPV vaccine by the 13th birthday.²¹ Continued monitoring of subsequent birth cohorts will be needed to assess receipt of the HPV vaccine by the 13th birthday. Efforts to promote an 11- to 12-year preventive check and annual health care visits, as well as use of all visits as opportunities for vaccination, likely will increase HPV vaccination initiation at the recommended age and catch-up vaccination.

There were no differences in HPV vaccination initiation rates according to racial/ethnic group; however, income and insurance status were significantly associated with beginning the vaccine series. The HPV vaccination initiation rate was highest among girls from households with the lowest incomes, the majority of whom were Medicaid-eligible, had SCHIP, or were VFC-eligible and insured; the initiation rate was lowest among VFC-eligible, uninsured girls. The VFC program might be providing better access to HPV vaccination for VFC-eligible, insured girls, compared with girls with other forms of insurance held by non–VFC-eligible girls (ie, private, military, or other insurance). The HPV vaccine is one of the most expensive vaccines, costing $130 per dose in the private sector, and requires a 3-dose series.²² Because of costs and concerns about reimbursement, some providers might not stock or offer the vaccine,^11,23 which might contribute to lower vaccination rates among non–VFC-eligible girls. However, HPV vaccination is a covered benefit in the military health system. Few preventive visits, few provider recommendations, and parent and provider attitudes about vaccination might contribute to lower vaccination rates for this group.

Despite VFC eligibility, uninsured girls had the lowest vaccination initiation rate. Lack of insurance is a known risk factor for lack of preventive health care among adolescents²⁴ and low vaccination rates among young children.²⁵ For uninsured individuals, health care access is limited to public health facilities or services for which they can self-pay. With insurance, there are more opportunities to access a medical home or usual sources of care,^26,27 which have been associated with higher vaccination rates.²⁸ A previous study demonstrated that VFC-eligible children with no medical home were less well vaccinated than VFC-eligible children with a medical home.²⁹ These observations might explain the higher initiation rate among VFC-eligible, insured girls, compared with VFC-eligible, uninsured girls and girls who received all of their vaccines at public facilities. Increasing the proportion of adolescents with health insurance, a primary care physician, and a usual source of care likely would improve health care access and continuity of services.³⁰ Improved outreach to uninsured adolescents and referrals to VFC providers also might improve vaccination coverage among uninsured girls.

Approximately one-half of the girls who initiated the HPV vaccination series completed it. Reasons for low completion rates might include poor communication of the need for a 3-dose series, failure of patients and parents to return for subsequent doses, fewer health care visits made by adolescents, and lack of a regular source of care. Although VFC-eligible, insured girls were more likely to initiate the HPV vaccination series than were girls with private insurance, fewer completed the series, compared with girls with private insurance. Implementing clinical practice guidelines to use reminder/recall systems likely would increase HPV vaccination series completion rates,³² particularly for girls who are VFC-eligible and insured or who receive vaccinations in public settings. There were no differences in HPV vaccination initiation rates according to race/ethnicity; however, we found disparities in HPV vaccination completion rates for some racial/ethnic groups. Black and Hispanic girls were less likely than white girls to complete the series. Higher completion rates among black and Hispanic girls might decrease disparities in cervical cancer morbidity and mortality rates,³³ which emphasizes the need for targeted efforts to increase HPV vaccination completion rates; however, additional research is needed for an understanding of the reasons for disparate completion rates for some groups.

Among unvaccinated girls, ∼40% of parents reported that they were unlikely to have their daughters vaccinated in the next 12 months and 10% were unsure. The lack of knowledge about the HPV vaccine and reports of daughters not being sexually active demonstrate the need for parental education on adolescent risks for HPV infection, stressing the benefits of vaccination and promoting the importance of vaccination before exposure. As in previous studies, few parents (<1%) reported concerns about increased sexual activity by their daughters after vaccination.^34,35

This analysis has some limitations. NIS-Teen is a random-digit-dialed survey and is limited to households with landlines. Findings might not be representative of households without landlines and households with only wireless telephones, which would contribute to noncoverage bias. According to data from the 2009 National Health Interview Survey, the number of wireless-only households is increasing; 25.9% of children currently live in wireless-only households.³⁶ Only 2.4% of children live in households without telephone service.³⁶ The National Health Interview Survey, a face-to-face household survey that includes landline, nonlandline, and wireless-only households, has been assessed for sociodemographic and health-related variables among adolescents. Benchmark comparisons of these variables for adolescents in the NIS-Teen and the National Health Interview Survey showed no significant evidence of coverage bias with adjustment of sampling weights for noncoverage of nonlandline and wireless-only households in the NIS-Teen.³⁷ Nonresponse bias might remain after weighting adjustments. Provider data or vaccination histories might be incomplete. We did not analyze other factors that might influence vaccine coverage, such as state policies. However, state was included in our analyses, to control for multiple unmeasured program factors likely related to the outcome variable. Further analyses will evaluate these program factors.