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Human papillomavirus vaccine uptake among 18- to 26-year-old women in the United States
National Health Interview Survey, 2010
Article first published online: 26 NOV 2012
Copyright © 2012 American Cancer Society
Volume 119, Issue 7, pages 1386–1392, 1 April 2013
How to Cite
Laz, T. H., Rahman, M. and Berenson, A. B. (2013), Human papillomavirus vaccine uptake among 18- to 26-year-old women in the United States. Cancer, 119: 1386–1392. doi: 10.1002/cncr.27894
- Issue published online: 18 MAR 2013
- Article first published online: 26 NOV 2012
- Manuscript Accepted: 11 OCT 2012
- Manuscript Revised: 9 OCT 2012
- Manuscript Received: 17 AUG 2012
- human papillomavirus;
- HPV vaccine;
- vaccine uptake;
- young adult women;
- cervical cancer
Human papillomavirus (HPV) vaccine uptake among young adult women has been reported to be very low. The authors conducted this study to provide an update on HPV vaccine uptake among 18- to 26-year-old women.
The authors used the National Health Interview Survey 2010 data to estimate HPV vaccine coverage and their correlates.
Overall, 22.7% of women initiated (≥1 dose) and 12.7% completed the vaccine (≥3 doses). Thus, about 56% of women who initiated the vaccine completed it. Multivariate logistic regression analyses showed that younger age, unmarried status, Papanicolaou test, influenza vaccine, lifetime vaccines, and HPV vaccine awareness were positively associated with receiving ≥1 and ≥3 doses. In addition, uninsured women were less likely to receive ≥1 dose (odds ratio [OR], 0.49; 95% confidence interval [CI], 0.28-0.84), and blacks (OR, 0.48; 95% CI, 0.23-0.99) and women with a family income <100% of the federal poverty level (OR, 0.40; 95% CI, 0.21-0.73) were less likely to receive ≥3 doses. Furthermore, based on vaccine initiators, blacks were less likely than whites to complete the vaccine (OR, 0.29; 95% CI, 0.16-0.55). Two thirds of unvaccinated women were not interested in future vaccination. Among those who were interested, >76.4% preferred to receive it free or at a lower cost, whereas 20% would pay the full cost of the vaccine.
One in 8 women completed the 3-dose HPV vaccine. Educational and vaccine financing programs are needed to improve the uptake among low-income minority women who are at increased risk for cervical cancer. Cancer 2013. © 2012 American Cancer Society.
Human papillomavirus (HPV) oncogenic strains (16 and 18) are known to be responsible for 70% of cervical cancer cases, whereas other low-risk types (6 and 11) account for 90% of genital warts in women.1, 2 The US Food and Drug administration (FDA) approved a quadrivalent HPV vaccine in 2006 that offers protection against HPV types 6, 11, 16, and 183 and a bivalent HPV vaccine in 2009 against HPV types 16 and 18.4 The Advisory Committee on Immunization Practices (ACIP) recommends routine vaccination for all US girls 11 to 12 years of age and catch-up vaccination for those 13 to 26 years old who were not previously vaccinated.3, 4 However, the efficacy of the vaccines is highest if given at a younger age before the onset of sexual activity.3, 4 Both vaccines have been demonstrated to have high efficacy (90%-100%) in preventing infections and precancerous lesions caused by vaccine type HPV among sexually active adolescents and young women who are naive to those strains.5-9
Studies based on clinical10-13 and national14-19 data have reported HPV vaccine uptake among young adult women since the vaccine was first approved in 2006. National studies conducted during 2007-2008 among young adult women have shown low vaccine initiation (9%-12%) and completion (6.2%)14-18; the series completion rate among those who initiated the vaccine was 53.8%.17 The objective of this study was to estimate HPV vaccine initiation (≥1 dose), completion (≥3 doses), completion of the vaccine series among those who initiated the vaccine, and their correlates among 18- to 26-year-old women using the National Health Interview Survey (NHIS) 2010 adult sample data.
MATERIALS AND METHODS
The NHIS is an in-person annual household survey with a cross-sectional design based on a nationally representative US noninstitutionalized civilian population sampled and selected through a complex, stratified, multistage probability design. Details of the survey methods used have been published elsewhere.17, 20 In 2010, the final sample size was 27,157 adults (>18 years), with a 60.8% response rate. For this study, we obtained data on women aged 18 to 26 years (n = 2011). All procedures were approved by the institutional review board of University of Texas Medical Branch.
This study focused on survey questions related to HPV vaccine awareness, receipt of the vaccine, number of doses, perceived barriers, and relevant sociodemographic variables based on 18- to 26-year-old women. Receipt of an unknown number of vaccine doses (n = 4) was included in the ≥1 dose (initiation) category, and 5 (n = 1) and 6 doses (n = 2) were included in the ≥3 doses (completion) category. The denominator for receipt of ≥1 dose and ≥3 doses analyses included all 18- to 26-year-old women, whereas the denominator for vaccine series completion among initiators analysis included only those who had initiated the vaccine (≥1 dose).
Women who had not received an HPV shot/vaccine or were refused by a physician when they requested the shot were asked whether they were interested in getting the HPV vaccine. Those who responded “no” or “don't know” were further asked about the main reason for not getting the vaccine. Those who responded “yes” to the above question were asked whether they would be willing to pay $360 to $500 for the vaccines. Those who responded negatively or those who mentioned cost of the vaccine as the main barrier for not getting vaccinated were further asked whether they would be willing to get the HPV vaccine free or at a much lower cost.
Sociodemographic characteristics were also assessed. Age (18-20 vs 21-26), race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, and others), region of residence (Northeast, Midwest, South, and West), immigration status (US born or not), education (<high school, high school, and >high school), marital status (married, living with partner, and unmarried/single), family income (≥200%, 100% to <200%, and <100% of the federal poverty level [FPL]), and type of health insurance (private, public, and none) were categorized for the purpose of analysis. Health care utilization covariates, such as any visit to an obstetrician/gynecologist/general physician or influenza vaccination in the previous year, Papanicolaou (Pap) test during the past 3 years, ≥1 lifetime vaccines (hepatitis A, B vaccine or tetanus shot in the past 10 years), and previous exposure to HPV were also assessed.
We used STATA 10 svy commands (STATA Corporation, College Station, Tex) for data analysis by incorporating probability sampling weights in conjunction with strata and primary sampling units generated by NHIS complex survey design. Percentages and 95% confidence intervals for HPV vaccine initiation (≥1 dose), completion (≥3 doses), and completion of the vaccine series among initiators were estimated by age groups (18-20 vs 21-26 years), sociodemographics, health care utilization, previous exposure to HPV, and HPV vaccine awareness.
We used chi-square tests for bivariate comparisons. Multivariate logistic regression analyses was used to examine the association between covariates of interest and the receipt of ≥1 and ≥3 doses of the HPV vaccine, and completion of the vaccine series among initiators. The variable “US born” was highly correlated with Hispanic ethnicity and was excluded from the multivariate analysis. Variables were screened, and candidate variables with P ≤ .20 with any dependent variable (uptake of ≥1 dose and ≥3 doses, and 3-dose vaccine series completion among initiators) were included in the final model.
A total of 94.1% (1892 of 2011) of 18- to 26-year-old women responded to the questions on HPV vaccination. Therefore, we limited our analysis to these 1892 women. Overall, 22.7% and 12.7% reported receiving ≥1 dose (n = 408) and ≥3 doses (n = 225), respectively. Thus, 56.2% women who initiated the vaccine completed the vaccine series (Fig. 1). Eighteen-year-old women had the highest rate of HPV vaccine uptake of ≥1 dose (44.4%), ≥3 doses (28.6%), and vaccine series completion among initiators (64.5%).
Bivariate analyses showed that 18- to 20-year-old women were more likely than those 21 to 26 years old to receive ≥1 dose and ≥3 doses of HPV vaccine (Table 1). Those who were white, US-born, single, covered by any public/private insurance, and high school graduates were more likely to receive ≥1 dose and ≥3 doses of vaccine compared with their counterparts. Women who were aware of the HPV vaccine, had seen an obstetrician/gynecologist/general physician in the past year, had received the influenza vaccine in the past year, and had ≥1 lifetime vaccines were more likely to receive ≥1 dose and ≥3 doses of the vaccine. In addition, women who had received a Pap test within the past 3 years were more likely to initiate the HPV vaccine. Bivariate analysis based on women who initiated the vaccine showed that black women were less likely to complete the vaccine series compared with whites, Hispanics, or Asians (P < .001; data not shown). Vaccine series completion among the initiators did not differ significantly by other covariates.
|Received ≥1 Dose||Received ≥3 Doses|
|Factor||Total, n = 1892a||Wgtd % (95% CI)||Pb||Wgtd % (95% CI)||Pb|
|18-20 years||499||36.1 (31.4-40.8)||21.6 (17.6-25.7)|
|21-26 years||1393||17.8 (15.6-20.0)||9.5 (7.8-11.2)|
|White||924||24.9 (22.0-27.8)||14.9 (12.5-17.3)|
|Black||374||18.8 (14.6-23.0)||5.9 (3.6-8.3)|
|Hispanic||456||18.1 (14.3-21.9)||9.6 (6.6-12.6)|
|Asian and otherd||138||19.5 (12.0-26.9)||15.8 (8.9-22.7)|
|Northeast||244||21.2 (15.6-26.7)||10.8 (6.6-14.9)|
|Midwest||442||24.4 (20.1-28.6)||14.0 (10.6-17.4)|
|South||702||19.8 (16.5-23.1)||11.3 (8.6-13.9)|
|West||504||26.5 (22.0-31.0)||14.9 (11.2-18.6)|
|Born in USA||.005c||.011c|
|Yes||1597||23.6 (21.3-25.9)||13.4 (11.6-15.3)|
|No||293||15.1 (10.4-19.7)||7.1 (4.1-10.2)|
|Less than HS||184||10.1 (5.1-15.0)||6.3 (2.1-10.5)|
|HS graduate/GED||417||18.0 (13.8-22.1)||8.4 (5.4-11.5)|
|Some college/college degree||1289||25.4 (22.8-28.1)||14.7 (12.6-16.8)|
|Married||362||12.3 (8.7-16.0)||5.8 (3.2-8.4)|
|Living with partner||240||12.9 (8.1-17.8)||7.3 (3.4-11.3)|
|Unmarried/single||1290||27.4 (24.6-30.1)||15.7 (13.4-17.9)|
|Family income, % of the federal poverty level||.237||.078|
|≥200%||688||24.2 (20.7-27.7)||14.6 (11.7-17.5)|
|100% to <200%||399||19.1 (14.8-23.5)||11.1 (7.6-14.7)|
|<100%||644||22.2 (18.6-25.8)||11.0 (8.3-13.8)|
|Private||894||28.2 (25.0-31.4)||17.1 (14.4-19.8)|
|Public||504||20.1 (16.1-24.3)||9.9 (6.9-12.9)|
|None||486||12.7 (9.5-16.0)||5.6 (3.6-7.8)|
|Health care utilization|
|Visit to OB/GYN/general physician in the past year||<.001c||<.001c|
|Yes||1441||25.4 (22.9-27.9)||14.3 (12.3-16.3)|
|No||449||12.7 (9.3-16.2)||7.0 (4.3-9.7)|
|Pap test in the past 3 years||.010c||.086|
|Yes||1424||23.9 (21.5-26.3)||13.4 (11.5-15.4)|
|No||456||19.0 (14.8-23.2)||10.5 (7.2-13.8)|
|Influenza vaccine in the past yeare||<.001c||<.001c|
|Yes||323||31.0 (25.4-36.6)||17.7 (13.0-22.3)|
|No||798||14.7 (12.0-17.4)||9.2 (6.9-11.4)|
|One or more lifetime vaccinesf||<.001c||<.001c|
|Yes||1515||25.4 (23.0-27.9)||14.4 (12.5-16.4)|
|No||315||8.7 (5.3-12.2)||3.4 (1.4-5.4)|
|Previous exposure to HPV|
|Ever had abnormal Pap test results/HPV infection||.059||.577|
|Yes||284||30.8 (24.9-36.7)||16.9 (12.0-21.8)|
|No||1212||24.5 (21.9-27.2)||14.1 (12.0-16.3)|
|HPV vaccine awareness|
|Ever heard of HPV vaccine||<.001c||<.001c|
|Yes||1359||28.9 (26.2-31.5)||16.4 (14.2-18.6)|
|No||526||3.1 (1.4-4.9)||1.1 (0.1-2.0)|
After adjusting for covariates, multivariate logistic regression models showed that women 21 to 26 years of age were less likely than 18- to 20-year-olds to receive ≥1 dose and ≥3 doses of the HPV vaccine (Table 2). Uninsured women were less likely than privately insured women to receive ≥1 dose of the vaccine. The likelihood of receiving ≥3 doses were less among black women than whites, and among women with a family income <100% of the FPL than those with family income ≥200% of FPL. Other characteristics positively associated with receiving both ≥1 dose and ≥3 doses of vaccine were: unmarried/single status, Pap test within the past 3 years, influenza vaccine in the past year, 1 or more lifetime vaccines, and HPV vaccine awareness. A separate multivariate analysis based on women who initiated the vaccine showed that black women were less likely than whites to complete the vaccine series (P < .001; data not shown).
|Factor||Received ≥1 Dose, OR (95% CI)a||Received ≥3 Doses, OR (95% CI)a|
|21-26 years||0.30 (0.19-0.45)b||0.31 (0.19-0.52)b|
|Black||0.94 (0.54-1.62)||0.48 (0.23-0.99)b|
|Hispanic||1.29 (0.75-2.22)||0.70 (0.34-1.43)|
|Asian and otherc||1.07 (0.49-2.35)||1.67 (0.72-3.87)|
|Midwest||1.01 (0.54-1.87)||1.76 (0.77-4.02)|
|South||0.68 (0.37-1.27)||1.67 (0.73-3.84)|
|West||1.37 (0.74-2.53)||2.21 (0.97-5.03)|
|Living with partner||0.93 (0.40-2.14)||0.62 (0.18-2.14)|
|Unmarried/single||3.10 (1.71-5.60)b||3.78 (1.74-8.20)b|
|Family income, % of the federal poverty line|
|100% to <200%||0.76 (0.46-1.25)||0.77 (0.43-1.40)|
|<100%||0.64 (0.39-1.03)||0.40 (0.21-0.73)b|
|Public||0.81 (0.48-1.36)||0.88 (0.45-1.71)|
|None||0.49 (0.28-0.84)b||0.52 (0.26-1.04)|
|Health care utilization|
|Pap test in the past 3 years|
|Yes||1.84 (1.09-3.10)b||2.44 (1.28-4.64)b|
|Influenza vaccine in the past yeard|
|Yes||2.32 (1.58-3.40)b||1.69 (1.06-2.70)b|
|One or more lifetime vaccinese|
|Yes||1.98 (1.00-3.91)b||3.04 (1.04-8.85)b|
|HPV vaccine awareness|
|Ever heard of HPV vaccine|
|Yes||8.80 (4.12-18.80)b||6.86 (2.41-19.54)b|
Overall, 77.3% of 18- to 26-year-old women were not vaccinated (n = 1478). Of the unvaccinated women, 68.6% were not interested or were unsure about receiving the vaccine in the future. The main reasons cited were: “do not need the vaccine” (39.6%), insufficient knowledge about the vaccine (12.7%), concerns about its safety (12.0%), not recommended by their physician (7.2%), not sexually active (6.7%), and too old for the vaccine (3.1%) (Table 3). Only 2.6% reported expense as a barrier. Uninsured women were more likely than privately insured women to have insufficient knowledge about the vaccine (P = .020). Of those (31.4%) who were interested in vaccination, 20% would be willing to pay full costs for the vaccine, 76.4% would prefer to receive it free or at much lower cost, and 3.4% would not even receive the free vaccine. Privately insured women were more likely to agree to pay full vaccine cost (P = .005), whereas uninsured women were more likely to prefer receiving the vaccine free or at a much lower cost (P = .037) compared with their counterparts.
|Insurance Coverage, Wgtd %||Family Income, % of Federal Poverty Levelc Wgtd %|
|Reasona||Total, n = 988b||Private, n = 445||Public, n = 263||None, n = 276||Pd||≥200%, n = 363||100% to <200%, n = 206||<100%, n = 324||Pd|
|Do not need||39.6||39.5||37.0||41.8||.475||42.2||39.5||36.2||.393|
|Do not know enough||12.7||10.2||14.5||16.2||.020e||10.5||13.7||15.3||.086|
|Worried about safety||12.0||14.8||10.6||8.1||.192||11.2||12.6||13.3||.859|
|Doctor did not recommend||7.2||7.8||8.6||4.9||.606||8.7||6.8||5.5||.571|
|Not sexually active||6.7||8.3||4.6||5.8||.076||5.5||7.2||8.1||.495|
|Too old for vaccine||3.1||2.6||2.1||5.3||.624||4.0||1.9||2.5||.495|
|Already have vaccine||2.9||2.6||4.1||2.5||.637||2.4||3.1||3.3||.907|
|Do not know||1.8||0.7||2.7||3.2||.006e||0.8||2.2||3.0||.063|
In this study, we observed that the overall rate of receiving ≥1 dose (22.7% vs 11.7%) and ≥3 doses (12.7% vs 6.2%) of HPV vaccine among 18- to 26-year-old women almost doubled when compared with NHIS 2008 survey results.17 Consistent with the NHIS 2008 study, the likelihood of vaccine initiation (received ≥1 dose) was significantly higher among 18- to 20-year-old women (36.1% vs 20.9%) compared with 21- to 26-year-old women (17.8% vs 7.9%), and the highest initiation rate was among 18-year-old women (44.4% vs 25.6%). This could be due to the finding that uninsured or underinsured women <19 years of age are eligible for the federally funded Vaccines for Children (VFC) program, whereas 19- to 26-year-old women are not eligible for most federal and state vaccine financing programs.14, 17, 21, 22
Although the rate of receiving ≥1 dose (initiation) of the vaccine has increased among 18- to 26-year-olds since 2008, it is still lower than that observed among 11- to 17-year-olds based on the NHIS 2010 study (22.7% vs 28.9%).23 The VFC program has been labeled as a major contributor for improving the HPV vaccine initiation rate among uninsured/underinsured adolescents younger than 19 years.24, 25 However, uptake of ≥3 doses (completion) of the vaccine among young adult women was comparable to that of adolescent girls in 2010 (12.7% vs 14.2%), as the rate of vaccine series completion among initiators was higher among 18- to 26-year-old women than 11- to 17-year-old adolescents (56.2% vs 49.2%).23 The slightly higher rate of 3-dose vaccine completion among young adult women than adolescents may be due to higher motivation of those aged >18 years to complete the vaccine series on their own initiative rather than parents' willingness or ability.17
HPV vaccine series completion has been reported to be essential for longer duration of protection against HPV infections.26 However, we observed that 44% of women who initiated the vaccine did not complete the series. Other studies among adolescents and young adult women also observed similar incomplete immunization rates.17, 23, 24, 27 This is inefficient for the patient and health care system, as 1 dose has not been shown to provide immunity. Thus, after the initiation of the vaccine series, coordinated efforts from both providers and vaccine initiators are needed to complete the vaccine series.28, 29 Knowledge, motivation, positive attitudes toward vaccination, and financial resources of the recipients have been shown to be important factors in determining who receives subsequent doses after initiation.28
We observed that uninsured women were less likely than privately insured women to initiate the vaccine. Lack of insurance was labeled as a major barrier to HPV vaccination among young adult women due to the high cost of the vaccine series.11, 14, 16, 17, 30 Low vaccination rates among this population are especially concerning, as their utilization of cervical cancer screening (Pap test) is also very low.31 Thus, they are at risk of invasive cervical cancer. In our study, of those willing to get the vaccine, uninsured women were more likely than privately insured women to prefer it at a lower cost. Thus, extension of the federal VFC financing program for 19- to 26-year-old women would increase the uptake rate among this age group. Alternatively, state governments could consider providing free vaccines within the existing setting of cancer prevention programs (breast and cervical cancer screening) for low income adult women.22
Consistent with the NHIS 2008 report,17 after adjusting for confounders, we found that receiving ≥1 dose of the vaccine did not differ significantly across racial and ethnic groups. However, black women were less likely than whites to receive ≥3 doses of the vaccine and complete the vaccine series among initiators. Similar findings were observed among young adult women within a university-based clinical system21, 30 and in several other studies.29, 32, 33 The lower likelihood of completing vaccine series among this population is concerning, given that the incidence of and mortality from cervical cancer is higher among black women than whites.34, 35 Several studies identified beliefs, attitudes, and neighborhood levels of education as possible reasons for this racial disparity in vaccine series completion.32, 33 Dempsey et al suggested that cultural mediators may be barriers to the compliance with vaccination among minority women.21 Thus, educational programs focused on increasing vaccination rates must use culturally relevant materials to improve vaccination compliance among this population.
Similar to other studies,14, 17 we also observed that unmarried and single young women were more likely than married women or women living with partner to receive ≥1 and ≥3 doses of the vaccine. This could be due to the finding that unmarried women are more likely to perceive the risk for HPV infection and the benefits of being vaccinated. Moreover, consistent with other studies,12, 17, 23, 27 we observed that preventive health behaviors including having had a Pap test in the past 3 years, influenza vaccination, and lifetime vaccines are significantly associated with receiving any and all 3 doses of the HPV vaccine among young adult women. This association most likely reflects overall attitudes among young women regarding preventive health services and suggests that this may be the easiest population to reach. Thus, a visit for any type of preventive health care may provide an opportunity to discuss the importance of HPV vaccination.
This study has several limitations. First, the NHIS survey data may be subjected to recall bias, as they are self-reported. Moreover, information on vaccine receipt and doses were not confirmed by provider immunization records. Second, as this survey did not assess sexual behaviors, we were unable to examine the association between these behaviors and receipt of the vaccine. Third, we could not evaluate whether the 3 doses were completed within the ACIP-recommended time frame due to lack of data on vaccination dates. Finally, we are unable to conclude causality, as the survey was cross-sectional in design. Despite these limitations, this study meaningfully estimated the recent uptake of this vaccine among young adult women based on a representative sample.
More than ¾ of young adult women remained unvaccinated in the United States, and an additional 10% were incompletely vaccinated. Furthermore, ⅔ of the unvaccinated women were not interested in receiving the vaccine in the future, mainly due to their negative attitudes toward vaccination, inadequate knowledge, and lack of physician recommendation. Of those who were interested, the majority preferred to get it free or at a much lower cost. Therefore, educational programs and public vaccine financing programs are needed for uninsured young women to expand HPV vaccination coverage among this age group in the United States.
The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) provided support for this study with 2 awards: a midcareer investigator award in patient-oriented research (K24HD043659; principal investigator [PI], A.B.B.) and an institutional training grant (T32HD055163; PI, A.B.B.) that supported T.H.L. as a National Research Service Award postdoctoral fellow. The authors are solely responsible for the contents, which do not necessarily represent the official views of the NICHD or the National Institutes of Health.
CONFLICT OF INTEREST DISCLOSURES
The authors made no disclosures.
- 3Quadrivalent human papillomavirus vaccine: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2007; 56: 1-24., , , , , .
- 4Centers for Disease Control and Prevention. FDA licensure of bivalent human papillomavirus vaccine (HPV2, Cervarix) for use in females and updated HPV vaccination recommendation from the Advisory Committee on Immunization Practices (ACIP). MMWR Morb Mortal Wkly Rep. 2010; 59: 626-629.
- 18Centers for Disease Control and Prevention. Vaccination coverage estimates from the National Health Interview Survey: United States, 2008. NCHS Health E-Stats 2009. Available at: http://www.cdc.gov/nchs/data/hestat/vaccine_coverage/vaccine_coverage.pdf Accessed June 5, 2012.
- 19Centers for Disease Control and Prevention. Adult vaccination coverage—United States, 2010. MMWR Morb Mortal Wkly Rep. 2012; 61: 66-72.
- 20National Center for Health Statistics. National Health Interview Survey (NHIS), 2010. Public use data release: NHIS survey description. Available at: ftp://ftp.cdc.gov/pub/Health_Statistics/NCHS/Dataset_Documentation/NHIS/2010/srvydesc.pdf Accessed June 5, 2012.
- 24Centers for Disease Control and Prevention. National, state, and local area vaccination coverage among adolescents aged 13-17 years—United States, 2008. MMWR Morb Mortal Wkly Rep. 2009; 58: 997-1001.
- 25Centers for Disease Control and Prevention. National and state vaccination coverage among adolescents aged 13 through 17 years—United States, 2010. MMWR Morb Mortal Wkly Rep. 2011; 60: 1117-2011.
- 26Merck & Co. A program to help improve patient compliance: 3 is key. 2010. Available at: http://www.merckvaccines.com/vaccines/gardasil/compliance_one.html Accessed June 5, 2012.
- 35National Cancer Institute. SEER stat fact sheets: cancer of the cervix uteri. Available at: http://seer.cancer.gov/statfacts/html/cervix.html Accessed June 5, 2012.