Nationally, vaccination coverage was <60.0% for all three of these recently recommended vaccines among both VFC-eligible and non-VFC-eligible adolescents. Coverage for each vaccine varied widely by geographic area in both groups, with several grantee areas having the majority of adolescents vaccinated with MCV4 or Tdap; only one area surveyed had attained ≥60.0% coverage for the three-dose HPV4 series. National coverage rates for MCV4 and Tdap were significantly lower among VFC-eligible vs. non-VFC-eligible adolescents, a pattern repeated in many grantee areas. Coverage with one or three doses of HPV4 vaccine was similar among VFC-eligible and non-VFC-eligible adolescents nationally, but significantly lower among VFC-eligible vs. non-VFC-eligible adolescents in several grantee areas. Although coverage for recommended adolescent vaccines is progressing steadily,22
underserved adolescents are lagging behind.
There are several potential reasons for coverage variations at the state or local level. During the period of increasing coverage that follows a new vaccine recommendation, differences in the pace of implementation are easily seen in variation of coverage levels. Immunization resources vary by state, and implementation of new vaccine recommendations in the public and private sectors may be delayed while funds are sought to cover the high cost of vaccine purchase.23–25
A recent study showed state- and county-level poverty rates are associated with geographic variation in HPV4 coverage, although associations differed in direction.26
Reimbursements for vaccines and vaccine administration also vary widely by state in both the public and private sectors;13,27
previous research suggests that provider reimbursement levels may help explain some state-level variation in vaccination coverage.28
Finally, state and local policies—for example, laws requiring adolescent vaccines for school entry—may affect vaccination coverage. For the 2009–2010 school year, 27 states required Tdap vaccination for middle-school entry, seven required MCV4, and two required HPV4 (but allowed students to opt out of this requirement).22
Coverage among VFC-eligible adolescents was lower than coverage for non-VFC-eligible adolescents in our sample for MCV4 and Tdap. Although VFC provides vaccines free of charge to eligible adolescents, costs associated with office visits are not covered by the program. The association of poverty level with adolescent vaccination coverage is inconsistent;22,29
however, studies have shown significantly lower rates of well-child visits8
and vaccination coverage29,30
among uninsured adolescents, independent of poverty status. In our sample, 61% of VFC-eligible adolescents lived below 133% of the federal poverty level, and 20% were uninsured. Nonfinancial barriers to vaccination may also deter poor or uninsured adolescents from making the preventive visits where vaccines are administered. These barriers may vary by location: adolescents in upstate New York did not report distance- or transportation-related barriers to accessing health care,7
but transportation was a substantial barrier to vaccination for poor mothers of young children in urban and rural North Carolina.31
It is also possible that VFC-eligible adolescents are unaware of their eligibility for free vaccines through VFC and are, therefore, less likely to seek vaccination services.
Finally, it should be noted that VFC-eligible adolescents differ from non-VFC-eligible adolescents on demographic characteristics that may be associated with vaccination coverage, including race/ethnicity, maternal age, and maternal education level. VFC eligibility is a marker not only for economic differences, but also for a constellation of factors that may contribute to limited use of preventive services, including vaccines.
Overall, 93% of VFC-eligible adolescents received vaccinations from a provider enrolled in the VFC program, suggesting that VFC is effectively reaching the financially vulnerable adolescents the program was designed to serve. However, access to VFC benefits varies widely by state, primarily due to differences in state income requirements for Medicaid eligibility. The proportion of Medicaid-enrolled adolescents in each grantee area ranges from less than 5% to more than 50%. Because Medicaid eligibility is the most common way for an adolescent to become VFC-eligible, this variation has a significant effect on the number of underserved adolescents who are able to access free vaccination services in different areas of the country. Interestingly, VFC-eligible adolescents were less likely than non-VFC-eligible adolescents to have received all vaccine doses in a private provider office, despite the fact that private providers comprise more than 70% of all VFC providers.32
In our sample, HPV4 coverage was similar among VFC- and non-VFC- eligible adolescents. Eight months after HPV4 vaccine was recommended for routine vaccination of adolescent females, nearly 90% of immunization programs were providing HPV4 vaccine to VFC providers.33
Conversely, it is known that many private providers delayed purchase of HPV4 vaccine due to financial concerns.24
A 2007 survey in North Carolina found practices participating in VFC were more likely than those not participating to have HPV4 vaccine available for their patients.34
Despite the success of VFC in making HPV4 vaccine available to vulnerable populations, limited access to care among underserved adolescents could impede completion of the three-dose series required for full protection. A recent study showed the majority of adolescent females would need multiple additional health-care visits to complete the HPV4 vaccination series.35
Such additional visits may represent a substantial financial burden for VFC-eligible adolescents, as uninsured adolescents pay a much greater proportion of their health-care expenses out of pocket than publicly or privately insured adolescents.36
However, in our sample, three-dose HPV4 coverage did not differ by VFC eligibility status, although series completion rates were low for all adolescent females. Further research is needed to determine what policies, practices, or public health messages contributed to this equality in coverage and whether these interventions might be applied to reduce coverage differences for other recommended adolescent vaccines.
Our results were subject to certain limitations. First, statistical adjustments made to these telephone survey data may not fully account for bias due to nonresponse or lack of landline telephone coverage. Limitations of the NIS methodology have been described previously.20
Second, vaccine receipt was determined solely by provider records; incomplete records may have resulted in underestimations of coverage. Third, VFC eligibility was determined using self-reported, point-in-time insurance status, although insurance status may vary from year to year or even month to month. Fourth, we were not able to measure some factors that may have affected vaccination coverage, such as vaccine availability or provider recommendations for vaccination. Finally, small sample sizes at the grantee area level resulted in potentially imprecise estimates of vaccination coverage with wide confidence intervals. This imprecision limited our ability to compare vaccination rates between VFC- and non-VFC-eligible adolescents at the grantee area level, particularly for HPV4, which is measured only among females. Grantee-level results should be interpreted with caution.