HPV Vaccine Dosing Schedule Adherence, Completion Low

Major Finding: Independent predictors of vaccine series completion were white (vs. black) race (odds ratio, 2.04 at 7 months; 1.92, at 12 months); use of contraception that required IM injection every 3 months (OR, 1.53 at 7 months; 2.06 at 12 months); and private vs. public insurance (OR, 1.31 at 7 months; 1.16 at 12 months).

Data Source: A retrospective study of health information records for 3,297 female patients (aged 9–26 years) who initiated HPV vaccination at a pediatric academic medical center.

Disclosures: Dr. Widdice said she has received research support through the investigator-initiated studies program of Merck & Co. for research unrelated to this study. Another author on the study, Dr. Jessica A. Kahn, is a co–principal investigator of a National Institutes of Health–funded clinical trial of HPV vaccine in HIV-infected adolescents, for which Merck is providing HPV vaccine and immunogenicity testing. The other investigators said they had no relevant financial disclosures. This study was funded by the NIH.

More than half of the doses of human papillomavirus vaccine received by 3,297 girls and young women undergoing vaccination at an academic medical center were received late, and the three-dose vaccine series completion rate was only 14% by 7 months and 28% by 12 months, according to a retrospective medical records study.

Adherence to the recommended interval of 2 months between the first and second dose was 28.5%, and adherence to the recommended intervals of 12 weeks between the second and third dose, and 6 months between the first and third dose was only 19.7% and 13.3%. Adherence to all three intervals was just 11.5%, Dr. Lea E. Widdice of Cincinnati Children's Research Foundation and her colleagues reported (Pediatrics 2011;127:77-84)

The average time between dose one and two was about 6 months, and the average time between dose one and three was 11 months, the investigators noted.

Independent predictors of vaccine series completion were white (vs. black) race (odds ratio, 2.04 at 7 months; 1.92 at 12 months); use of contraception that required intramuscular injection every 3 months (OR, 1.53 at 7 months; 2.06 at 12 months); and private (vs. public) insurance (OR, 1.31 at 7 months; 1.16 at 12 months), they found. Age did not predict adherence.

The investigators reviewed the health information records of all 9- to 26-year-old girls and women who initiated vaccination at Cincinnati Children's Hospital Medical Center from November 2006 to June 2008.

“Understanding adherence to the HPV4 recommended vaccination schedule, and identifying factors that predict completion among adolescents who initiate vaccination are necessary to develop evidence-based strategies to increase adherence among adolescents,” Dr. Widdice and her associates wrote.

The findings are of concern because although the vaccine has been shown in clinical trials to be 94%–100% effective, the duration of protection and efficacy in those who don't complete the vaccine series or who receive doses at intervals different from those in the clinical trials are currently unknown, and because the decreased likelihood of series completion among black subjects – who comprised about two-thirds of the study subjects – could exacerbate existing disparities in cervical cancer, the investigators said.

“In future studies, factors that underlie the association between race and completion of the HPV4 series should be examined,” they wrote, adding that the health care community should be vigilant in providing education and access to all patients.

Future studies also should compare immunization status for HPV and other diseases in adolescents, should aim to understand rates of and reason for not initiating vaccination in an effort to optimize HPV4 vaccine coverage, and should assess factors related to HPV vaccine adherence in male patients now that there is a “permissive recommendation” for use in that population and since factors could differ between male and female patients, they said.

In this study, compared with HPV4 vaccine clinical trials, the mean completion rates were lower, and the mean intervals between doses were longer.

“Clinical improvement efforts should focus on timing of the second dose as well as completion of three doses,” Dr. Widdice and her associates added.