The proportion of insured girls and young women completing the human papillomavirus (HPV) vaccine among those who initiated the series has dropped significantly -- as much as 63 percent -- since the vaccine was approved in 2006, according to new research from the University of Texas Medical Branch (UTMB) in Galveston.

The study, published in the current issue of Cancer, reveals the steepest decline in vaccine completion among girls and young women aged nine to 18 -- the age group that derives the greatest benefit from the vaccine, which should be administered in three doses over six months.

"The first generation of women that could benefit from the only HPV-related cancer vaccine in existence is missing the opportunity," said lead author Abbey B. Berenson, director of the Center for Interdisciplinary Research in Women's Health (CIRWH) at UTMB. "This vaccine prevents one of the most devastating cancers in women."

Researchers examined a large health insurance company's records of 271,976 female patients aged nine and older who received the first dose of the HPV vaccine between 2006 and 2009. Of this full sample, just 38.2 percent received all three doses within 365 days. In all but one age group (27 and older), researchers uncovered a marked drop in the number of females who completed the vaccine series:

HPV Vaccine Completion Rates

    Age 2006 2009 Completion Dec/Inc
    9-12 57.5% 21.2% -- 63%
    13-18 54.9% 20.8% -- 62%
    19-26 44.3% 22.6% -- 49%
    27+ 15% 24.5% + 37%

Source: UTMB

Berenson said that among the 9-12 and 13-18 age groups, the drop may be at least partly attributable to parents not being accustomed to taking older children to the doctor more than once or twice each year and rarely making appointments for this age group solely around vaccines. The slight completion increase among patients 27 and older may be because these women are responsible for their own health care appointments and decisions. They also may have benefited from more doctors offering the vaccine to women older than the recommended age group in the years following FDA approval.

Approved by FDA in 2006, the HPV vaccine is administered as a three-dose series over six months and is effective in preventing infection with certain HPV strains associated with the development of cervical cancer, which affects nearly half a million women worldwide each year and kills more than a 250,000. It also protects against anal, penile and some head and neck cancers as well as genital warts. Berenson added that the vaccine also allows women to avoid the anxiety that comes along with an abnormal Pap smear. The efficacy and duration of protection are proven for only a complete vaccination; the efficacy of only one or two doses is not well established.

In addition to the declining completion rates, researchers found that girls who received the first dose from a gynecologist or obstetrician were more likely to complete the vaccine series than those who received the first dose from a pediatrician.

They also observed an increase in the proportion of female patients who received only the first vaccine dose compared to those who received two or three, indicating that providers are encouraging initiation of the vaccine series but are not following up about the second and third doses.

"It appears that patients and parents do not understand that all three shots of the vaccine are required for HPV protection, and that perhaps physicians are not doing a good enough job of educating and reminding patients to ensure completion," she said. Berenson added that the high cost of the vaccine, one of the commonly cited barriers, was not a likely issue for this group as all were covered by health insurance.

Berenson recommended that better communication with patients and parents about the required doses and scheduling follow up visits could be achieved via phone, email, text message or other methods convenient for both parties.

She underscored that it will be important for future studies to identify the barriers inhibiting patients' completion of the vaccine and solutions for how to overcome those barriers.