Objectives. We investigated whether maternal attitude toward prevention, as indicated by history of seeking Papanicolaou (Pap) tests and contracting sexually transmitted infections, influenced human papillomavirus (HPV) vaccine uptake among their adolescent daughters.

Methods. We linked the electronic health records of girls aged 9 to 17 years with their mothers at Kaiser Permanente Southern California (n = 148 350 mother–daughter pairs). Personal identifying information was removed from the data set after the matching of daughters and mothers was completed. We used logistic regression models to detect associations between mothers' history of Pap tests and abnormal results, genital or anal warts, and other sexually transmitted infections and daughters' HPV vaccine initiation and 3-dose regimen completion.

Results. Mothers' testing history was associated with daughters' likelihood for vaccination across ethnic and neighborhood socioeconomic strata (overall odds ratio [OR] = 1.47; 95% confidence interval [CI] = 1.43, 1.52). Mothers' history of sexually transmitted infections was only modestly associated with daughters' vaccination. Mothers' testing history was positively associated with daughters' regimen completion (overall OR = 1.42; 95% CI = 1.31, 1.54).

Conclusions. Mothers' attitude toward prevention may influence HPV vaccine uptake among adolescent girls. The impacts of targeting mothers should be considered by HPV vaccination programs and investigated by further research.

The quadrivalent human papillomavirus vaccine (HPV4), Gardasil (Merck & Co, Whitehouse Station, NJ), has been shown to be efficacious in preventing cervical cancer and other conditions caused by HPV types 6, 11, 16, and 18.1,2 The vaccine is indicated for girls and women aged 9 to 26 years and is given in 3 injections over 6 months.3 The Advisory Committee on Immunization Practice (ACIP) recommends vaccinating adolescent girls before they become sexually active.3 Because of concern that vaccinating against HPV may condone or promote sexual activity in adolescent girls, integration of this procedure into clinical care has been somewhat controversial. Furthermore, the safety and long-term efficacy of the vaccine remain to be elucidated. This controversy and the fact that state law does not require the vaccine may impede its implementation in public health and clinical settings.

Parental consent is generally required for medical intervention given to adolescents younger than 18 years old,4 so parents' perceptions about sexuality, vaccination, and sexually transmitted infections (STIs) may play an important role in determining the uptake of the HPV vaccine among adolescent girls. Several studies on HPV and STI vaccine acceptability have reported that parental health beliefs about STIs, personal history of STIs, and knowledge about HPV are significant predictors of parental intent for vaccination.5,6

Because the HPV4 vaccine has potential public health importance, we investigated the hypothesis that uptake of HPV4 among girls aged 9 to 17 years is associated with their mothers' personal attitude about preventive measures related to cervical cancer as assessed by history of seeking Papanicolaou (Pap) tests and personal experience of STIs. We measured HPV4 uptake by initiation of the vaccination and completion of the 3-dose regimen within 1 year. We took advantage of the electronic health records available at Kaiser Permanente Southern California (KPSC), which allowed linkage of the medical records of mothers and daughters.

KPSC is the largest managed care organization in Southern California, serving more than 3 million members, who are diverse ethnically (43% White, 35% Hispanic, 9% African American, 10% Asian/Pacific Islander, and 3% other race) and socioeconomically (census block data indicate that 9% of KPSC members reside in neighborhoods with median household income < $30 000 and 19% in neighborhoods with median household income >$60 000). Members of KPSC are broadly representative in ethnic diversity and socioeconomic status (SES) of the general population in Southern California, and all members have relatively equal health care coverage. HPV4 vaccines are offered to eligible female members without additional out-of-pocket cost (variations in office visit copays exist but are small).

Study Sample

We selected female members of KPSC aged 9 to 17 years as of October 2006 and their mothers who were also members. October 2006 was chosen as the start of the investigation because HPV4 was approved for the KPSC vaccine formulary in September 2006 and began to be dispensed in October 2006. A total of 232 707 girls aged 9 to 17 years were members of the health plan in October 2006. The study period was October 2006 to September 2007 for HPV vaccine initiation and October 2006 to March 2008 for completion of the 3-dose regimen recommended by ACIP (a minimum of 4 weeks between doses 1 and 2 and 12 weeks between doses 2 and 3, with all doses given within 1 year of the first dose).

We linked girls and their mothers by 2 methods, one based on birth records and the other on family health plan membership. We first obtained the electronic records, including the unique Kaiser medical record number, of girls aged 9 to 17 years during the designated period. The records of girls who were born at KPSC hospitals contained their mothers' medical record number, allowing us to link each girl's medical records with her mother's. A total of 48 146 daughter–mother pairs were identified with this method. For girls who were not born at KPSC hospitals, we relied on family health plan subscription. Kaiser Permanente members may apply for health care coverage for their immediate family members (i.e., spouse and children). Records of family members who are enrolled in the KPSC plan through the primary health plan member are stored under the primary member's name in the Kaiser electronic database. We identified potential mothers of each girl as female members who were enrolled through the same primary member as the girl and who were at least 16 years older (to exclude sisters) but less than 45 years older (to exclude grandmothers).

Girls for whom no potential mother or multiple potential mothers were identified were excluded from the study. A total of 135 246 pairs were identified through family health plan membership. Personal identifying information was removed from the data set after the matching of daughter and mothers was completed.

To properly assess mothers' Pap test history, we excluded girls whose mothers had not been continuously enrolled in the health plan for at least 3 years before October 2006 (n = 32 846). The 3-year window reflected the US Preventive Service Task Force recommendation for cervical cancer screening,7 which was part of the KPSC clinical practice guidelines. We also excluded mothers and daughters whose demographic information was incomplete (n = 2196 mother–daughter pairs).

After these exclusions, 148 350 mother–daughter pairs were available for analyses. For analyses of regimen completion, we further limited the sample to girls who received the first dose of HPV4 between October 2006 and March 2007 (n = 19 729) and maintained their health plan membership for at least 12 months after receiving the first dose. This restriction allowed for a full year of follow-up for completion of the regimen and resulted in 18 275 mother–daughter pairs for these analyses.

Variables

Our outcomes of interest were (1) HPV4 initiation between October 2006 and September 2007 and (2) completion of the 3-dose regimen as recommended by ACIP. We obtained information on HPV4 vaccination through the Kaiser Immunization Tracking System. This system tracks all immunization and skin tests given at Kaiser Permanente and is the health plan's legal record for immunization. HPV4 vaccination records in the system were linked to the mother–daughter pairs through the daughter's unique medical record number. Date and dose of vaccination were available from the tracking system.

Mothers' attitudes about preventive measures against cervical cancer were represented by medical record documentation of Pap tests. Mothers' personal experiences of sexually transmitted infections were measured by history of abnormal Pap test result, genital or anal warts, and other STIs (chlamydia, gonorrhea, genital herpes, trichomoniasis, or syphilis). Mothers' histories of Pap tests and abnormal results were obtained from the KPSC electronic database of laboratory procedures. Mothers' Pap test histories were coded as a binary variable: no Pap tests or at least 1 Pap test in the 3-year window. Histories of genital or anal warts and other STIs were ascertained by computer search of diagnoses with corresponding International Classification of Diseases, Ninth Revision, codes specific to each condition.8

Girls' and mothers' age, race/ethnicity, and length of health plan membership were available from the KPSC membership files. We linked health plan members' addresses via geocoding with US census block data,9 which provided information on neighborhood education and income status. Medi-Cal (California state-subsidized program) status was also used as an indicator for SES. Specialties of girls' primary care providers were obtained from the Kaiser Permanente provider files.

Statistical Analyses

We first calculated the distributions of demographic variables and medical history of mothers by girls' HPV4 initiation status. Associations between these variables and HPV4 initiation were tested with standard methods, including analysis of variance and the χ2 test. To assess the generalizability of our study cohort, we also compared the demographic characteristics of the girls and mothers included in and excluded from the analyses.

We examined associations between HPV4 initiation and mothers' Pap test history, HPV history, and STI history in separate multivariable logistic regression models. All models were adjusted for girls' age, length of health plan membership, provider specialty, neighborhood SES (median household income and percentage of adults without a high school diploma), as well as mothers' age, race/ethnicity, and length of health plan membership. We also assessed the effect of further adjusting for Medi-Cal status. We explored interaction between mothers' Pap test history and mothers' HPV- or other STI-related medical history by including terms for both main effects and their 2-way interaction in the model. A P value of .05 was considered statistically significant.

We performed stratified analyses to test whether associations differed by race/ethnicity or by neighborhood SES. For neighborhood SES, we stratified analyses by 2 factors derived from the census block in which each girl resided: (1) whether at least 40% of households had household income of $20 000 or less and (2) whether at least 40% of adults aged 25 years or older lacked a high school diploma. The cut-off figure of$20 000 household income to indicate poverty was based on an average family size of 4 for families with children younger than age 18 years.10 Mothers' Pap test history and medical history of HPV and STIs were examined for associations in separate multivariable logistic regression models. In addition, analyses were stratified by race/ethnicity and neighborhood SES to evaluate the potential effect modification of these factors.

The demographic characteristics of the 148 350 girls included in the analyses are shown in Table 1. Their mean age was 13.2 years. Girls included in the study, on average, had been enrolled in the health plan significantly longer than those who were excluded and lived in neighborhoods with a higher average income (Table 1).

TABLE 1 Comparison of Demographic Characteristics of Girls Who Were Included (n = 148 350) and Excluded (n = 80 705) From the Study Sample: California, October 2006–September 2007

TABLE 1 Comparison of Demographic Characteristics of Girls Who Were Included (n = 148 350) and Excluded (n = 80 705) From the Study Sample: California, October 2006–September 2007

 Included, No. (%) or Mean ± SD Excluded, No. (%) or Mean ± SD P Age, y 13.2 ± 2.6 13.1 ± 2.6 <.01 Race/ethnicity <.01 White 27 052 (18.2) 5 657 (7.0) African American 10 855 (7.3) 3 615 (4.5) Hispanic 38 125 (25.7) 24 160 (29.9) Asian/Pacific Islander 5 739 (3.8) 1 425 (1.8) Other or unknown 66 579 (44.9) 45 848 (56.8) Census block adult education level, % No high school diploma 27.3 ± 19.6 32.7 ± 20.7 <.01 Any college 51.1 ± 20.9 45.6 ± 20.9 <.01 Census block median household income, $59 257 ± 26 541 52 128 ± 23 882 <.01 Length of health plan membership, y 9.4 ± 4.2 3.9 ± 4.2 <.01 Quadrivalent Human Papillomavirus Vaccination Initiation A total of 148 350 mother–daughter pairs were included in the analyses for HPV vaccine initiation. Table 2 shows the distributions of the demographic characteristics and mothers' HPV-related medical history among girls who initiated and those who did not initiate HPV4 in the assessment period. In the crude analysis, mothers of girls who initiated HPV4 vaccination were more likely to have had a Pap test in the past 3 years (82% versus 76%; P < .01). TABLE 2 Baseline Characteristics of Girls and Their Mothers, by Quadrivalent Human Papillomavirus Vaccine (HPV4) Initiation Status: California, October 2006–September 2007 TABLE 2 Baseline Characteristics of Girls and Their Mothers, by Quadrivalent Human Papillomavirus Vaccine (HPV4) Initiation Status: California, October 2006–September 2007  HPV4 Initiation No HPV4 Initiation P Daughters Age, y, mean (SD) 13.8 (2.1) 13.0 (2.7) <.01 Provider specialty, no. (%) Pediatrician 34 407 (85.4) 84 215 (77.9) <.01 Family medicine 2 687 (6.7) 9 821 (9.1) Other 3 194 (7.9) 14 026 (13.0) Length of health plan membership, y, mean (SD) 10.2 (4.2) 9.2 (4.1) <.01 Mothers Age, y, mean (SD) 42.1 (6.4) 41.3 (6.5) <.01 Race/ethnicity, no. (%) 9 255 (23.0) 24 195 (22.4) <.01 White 3 797 (9.4) 11 214 (10.4) African American 15 987 (39.7) 38 798 (35.9) Hispanic 2 749 (6.8) 6 846 (6.3) Asian/Pacific Islander 8 500 (21.1) 27 009 (25.0) Other or unknown % of census block adult education level, mean (SD) No high school diploma 27.7 (19.9) 27.2 (19.4) .01 Any college 51.1 (21.3) 51.1 (21.7) .72 Census block median household income,$, mean (SD) 60 092 (27 403) 58 940 (26 172) <.01 Length of health plan membership, y, mean (SD) 13.5 (7.8) 12.4 (7.4) <.01 Pap test in past 3 y, no. (no. per 1000 person-years) 33 131 (82.2) 81 841 (75.7) <.01 History of abnormal Pap test result,a no. (no. per 1000 person-years) 7 117 (18.0) 17 227 (17.1) <.01 History of genital/anal warts,a no. (no. per 1000 person-years) 1 065 (2.7) 2 357 (2.3) <.01 History of other STIs,ab no. (no. per 1000 person-years) 916 (2.3) 2 311 (2.4) .13

Note. Pap = Papanicolaou; STI = sexually transmitted infection. For HPV4 vaccine initiation, n = 40 288. For no HPV4 vaccination initiation, n = 108 062.

aAdjusted for length of membership with Kaiser Permanente.

bChlamydia, gonorrhea, genital herpes, trichomoniasis, or syphilis.

In multivariable analyses, a mother's Pap test history was associated with her daughter's HPV4 initiation (odds ratio [OR] = 1.47; 95% confidence interval [CI] = 1.43, 1.52; Table 3). We observed only modest associations between a girl's likelihood of HPV4 vaccination and her mother's history of an abnormal Pap test result (OR = 1.11; 95% CI = 1.07, 1.14), genital or anal warts (OR = 1.19; 95% CI = 1.10, 1.28), or other STIs (OR = 1.13; 95% CI = 1.04, 1.22). Further adjustment for Medi-Cal status did not change the associations. When we stratified by race/ethnicity, mothers' Pap test history was consistently associated with HPV4 initiation in all racial/ethnic groups (Table 3). These associations also were not modified by neighborhood income and education level (Table 3). We found no significant interactions between mothers' Pap test history and STI or genital wart diagnosis in predicting daughters' vaccination status.

TABLE 3 Odds Ratios (ORs) for Multiple Logistic Regression of Girls' HPV4 Initiation, by Mothers' History of Pap Tests and STIs: California, October 2006–September 2007

TABLE 3 Odds Ratios (ORs) for Multiple Logistic Regression of Girls' HPV4 Initiation, by Mothers' History of Pap Tests and STIs: California, October 2006–September 2007

 Pap Test in Past 3 y, OR (95% CI) History of Abnormal Pap Test Result, OR (95% CI) History of Genital/Anal Warts, OR (95% CI) History of Other STIs,a OR (95% CI) Overall (crude) 1.48 (1.44, 1.53) 1.13 (1.10, 1.17) 1.22 (1.13, 1.31) 1.07 (0.99, 1.15) Overallb 1.47 (1.43, 1.52) 1.11 (1.07, 1.14) 1.19 (1.10, 1.28) 1.13 (1.04, 1.22) Race/ethnicityb White 1.46 (1.38, 1.56) 1.05 (0.99, 1.12) 1.05 (0.91, 1.18) 1.29 (1.08, 1.54) African American 1.31 (1.19, 1.44) 1.07 (0.98, 1.16) 1.28 (0.97, 1.70) 1.13 (0.98, 1.32) Hispanic 1.41 (1.34, 1.48) 1.10 (1.05, 1.16) 1.14 (1.00, 1.31) 1.13 (0.99, 1.30) Asian/Pacific Islander 1.40 (1.24, 1.58) 1.07 (0.93, 1.22) 1.96 (1.42, 2.69) 1.32 (0.87, 2.01) Census block adult education levelbc High 1.46 (1.41, 1.52) 1.10 (1.07, 1.15) 1.18 (1.09, 1.29) 1.19 (1.09, 1.31) Low 1.51 (1.42, 1.61) 1.14 (1.07, 1.21) 1.27 (1.07, 1.50) 0.96 (0.83, 1.12) Census block median household incomebd High 1.46 (1.42, 1.51) 1.11 (1.07, 1.15) 1.19 (1.10, 1.28) 1.17 (1.07, 1.27) Low 1.57 (1.43, 1.72) 1.10 (1.00, 1.20) 1.21 (0.94, 1.57) 0.92 (0.75, 1.14)

Note. HPV4 = quadrivalent human papillomavirus vaccine; Pap = Papanicolaou; STI = sexually transmitted infection; CI = confidence interval.

aChlamydia, gonorrhea, genital herpes, trichomoniasis, or syphilis.

bFor each variable, the OR was adjusted for girl's age, length of health plan membership, provider specialty, neighborhood socioeconomic status (median income and percentage of adults without high school diploma), as well as mother's age, race/ethnicity, and length of health plan membership. Race/ethnicity was not in the model stratified by race/ethnicity. Neighborhood socioeconomic status was not in the model stratified by neighborhood income/education status.

cHigh education level was defined as more than 60% of adults 25 years and older having a high school diploma. Low education level was defined as at least 40% of adults 25 years and older lacking a high school diploma.

dHigh median household income was defined as more than 60% of households having an income above $20 000. Low median household income was defined as at least 40% of households having an income of$20 000 or less.

Regimen Completion

A total of 19 729 girls initiated HPV4 vaccination between October 2006 and March 2007, and 18 275 of them remained as Kaiser Permanente members for the next 12 months. Among the 18 275 girls included in the analyses for regimen completion, 7430 (41%) completed the 3-dose regimen within 1 year after initiation and complied with ACIP recommendations on time between doses. Two hundred eighty-three girls (1.5%) completed the 3 doses within 1 year but did not adhere to ACIP recommendations. Daughters whose mothers had had at least 1 Pap test in the past 3 years were more likely to complete the vaccination regimen (OR = 1.42; 95% CI = 1.31, 1.54; Table 4). A mother's history of abnormal Pap test result or genital or anal warts, but not other STIs, was also positively associated with her daughter's completion of the regimen. Further adjustment for Medi-Cal status did not change the associations.

TABLE 4 Odds Ratios (ORs) for Multiple Logistic Regression of Girls' Completion of HPV4 Regimen, by Mothers' History of Pap Tests and STIs: California, October 2006–September 2007

TABLE 4 Odds Ratios (ORs) for Multiple Logistic Regression of Girls' Completion of HPV4 Regimen, by Mothers' History of Pap Tests and STIs: California, October 2006–September 2007

 Pap Test in Past 3 y, OR (95% CI) History of Abnormal Pap Test Result, OR (95% CI) History of Genital/Anal Warts, OR (95% CI) History of Other STIs,a OR (95% CI) Overall (crude) 1.38 (1.27, 1.50) 1.11 (1.03, 1.20) 1.37 (1.15, 1.64) 0.96 (0.79, 1.16) Overallb 1.42 (1.31, 1.54) 1.16 (1.07, 1.24) 1.26 (1.05, 1.52) 1.07 (0.88, 1.31) Race/ethnicityb White 1.43 (1.22, 1.67) 1.20 (1.02, 1.41) 1.41 (1.01, 1.97) 1.38 (0.91, 2.10) African American 1.26 (0.96, 1.67) 1.01 (0.80, 1.28) 1.60 (0.87, 2.94) 0.67 (0.43, 1.04) Hispanic 1.35 (1.17, 1.55) 1.12 (0.99, 1.27) 1.07 (0.78, 1.47) 1.10 (0.79, 1.55) Asian/Pacific Islander 1.64 (1.14, 2.36) 1.29 (0.90, 1.84) 1.49 (0.73, 3.04) 4.92 (1.00, 24.25) Census block adult education levelbc High 1.49 (1.36, 1.64) 1.13 (1.03, 1.24) 1.25 (1.02, 1.53) 1.11 (0.88, 1.40) Low 1.27 (1.08, 1.51) 1.22 (1.04, 1.42) 1.41 (0.95, 2.11) 0.95 (0.64, 1.42) Census block median household incomebd High 1.44 (1.32, 1.57) 1.15 (1.06, 1.25) 1.32 (1.09, 1.59) 1.16 (0.94, 1.44) Low 1.40 (1.07, 1.83) 1.18 (0.93, 1.51) 1.04 (0.55, 1.95) 0.62 (0.34, 1.14)

Note. HPV4 = quadrivalent human papillomavirus vaccine; Pap = Papanicolaou; STI = sexually transmitted infection; CI = confidence interval.

aChlamydia, gonorrhea, genital herpes, trichomoniasis, and syphilis.

bFor each variable, the OR was adjusted for girl's age, length of health plan membership, provider specialty, neighborhood socioeconomic status (median income and percentage of adults without high school diploma), as well as mother's age, race/ethnicity, and length of health plan membership. Race/ethnicity was not in the model stratified by race/ethnicity. Neighborhood socioeconomic status was not in the model stratified by neighborhood income/education status.

cHigh education level was defined as more than 60% of adults 25 years and older having a high school diploma. Low education level was defined as at least 40% of adults 25 years and older lacking a high school diploma.

dHigh median household income was defined as more than 60% of households having an income above $20 000. Low median household income was defined as at least 40% of households having an income of$20 000 or less.

In stratified analyses, mothers' Pap test history was consistently associated with regimen completion in all racial/ethnic groups (Table 4). The association was not modified by neighborhood income or education level. Mothers' history of STIs showed some evidence of an inverse association with regimen completion in African Americans (OR = 0.67; 95% CI = 0.43, 1.04) and was strongly associated with increased odds of regimen completion in Asian/Pacific Islanders (OR = 4.92; 95% CI = 1.00, 24.25; Table 4). As with vaccine initiation, we found no significant interactions between mothers' Pap test history and their history of STIs or genital warts in predicting daughters' regimen completion.

We found several important relationships between a mother's Pap test and sexual health history and her adolescent daughter's vaccine initiation and completion of the vaccine regimen. Daughters who received the HPV4 vaccine during the assessment period were 50% more likely than those who did not to have mothers who had had a Pap test in the past 3 years. These findings support the hypothesis that mothers' attitudes about preventive measures such as the Pap test influence their adolescent daughters' uptake of the HPV vaccine. We found this to be true regardless of race/ethnicity, neighborhood income, or education.

Our findings for the relationship between daughters' uptake of HPV4 vaccine and their mothers' STI and genital warts histories were not as consistent as our Pap test findings. Several previous studies on STI vaccine acceptability suggest that parental history of STIs is correlated with intent for vaccination of the children against STIs.5,11,12 In our study, although mothers' history of STIs (including HPV-related conditions) was associated with HPV4 initiation, the associations were only modest and inconsistent across racial/ethnic groups and levels of SES.

In this early experience of HPV vaccination, overall regimen completion according to ACIP recommendations within a 1-year time frame was only 41%, suggesting the need to improve compliance with the recommended regimen. ACIP recommends that the 3 doses of HPV4 be given at day 0, month 2, and month 6, with a minimum of 4 weeks between doses 1 and 2 and 12 weeks between doses 2 and 3.3 Although the cause of failure to complete the full regimen is unclear, our results suggest that mothers' attitudes about preventive measures may play an important role in the return of their daughters to the clinic to complete the series of vaccinations. If confirmed by other studies, these findings suggest that mothers of adolescent girls are important targets for public health efforts aiming to increase protection against HPV through immunization.

We observed a potential modification of the associations between daughters' regimen completion and mothers' history of HPV-related conditions or other STIs by race and SES. For example, in African Americans, mothers' history of STIs was inversely associated with regimen completion. SES may explain part of this effect modification, because African American girls in our study tended to reside in neighborhoods with lower incomes (20% of African Americans, and only 3% of Whites, fell in our low-income neighborhood strata). However, other cultural or family factors may also have contributed to these observations in African Americans. Our findings suggest that there may be different mechanisms determining HPV4 regimen completion in different racial/ethnic groups.

Several potential limitations should be considered in the interpretation of our results. We were unable to identify the mothers for all eligible girls in our sample. Girls with an identified mother were more likely to live in a neighborhood of higher average income. The girls and their mothers may also have had a different race/ethnicity distribution than did those who were excluded from our analyses. This inclusion bias should inversely affect the generalizability of our results. However, the consistency of the OR estimates for mothers' Pap test history across strata of various ethnic groups as well as neighborhood SES indicators suggested that generalizability was not significantly impaired. On the other hand, stratum-specific estimates should be considered when interpreting findings for mothers' history of HPV-related conditions and other STIs.

Another limitation is that we used census block–level data to indicate SES, and this may not have accurately reflected individual-level SES. Finally, we used Pap test history to indicate a mother's attitude toward preventive measures. Although this may not always accurately reflect a woman's attitude, our result points to a marker of a mother's characteristic that may be useful for identifying girls at risk for failure to be vaccinated and for noncompliance with the regimen.

Despite these limitations, our study had several important strengths, including directly linking mothers' and daughters' medical records and vaccination status. The availability of longitudinal health records for all members of the managed care organization minimized the potential recall and selection biases that complicate studies relying on active participant recruitment. The ethnically and socioeconomically diverse member population of KPSC also allowed us to examine the association of interest among different subgroups of race/ethnicity and neighborhood SES.

Our findings suggest that mothers' attitudes toward preventive measures are one of the factors determining whether their daughters receive a nonmandatory vaccine against HPV infection and comply with its recommended 3-dose regimen. Should long-term studies determine that the vaccine is safe, clinicians may be encouraged by data such as ours to educate mothers of adolescent girls in their efforts to increase HPV vaccination rates and particularly rates of regimen completion.

## Human Participant Protection

The study protocol was approved by the Kaiser Permanente Southern California institutional review board.

# References

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