Targeting the human papillomavirus (HPV) vaccine to sexually active young adult women at greatest risk for contracting one or more of the HPV strains known to cause cervical cancer and genital warts might seem like an effective strategy.
But a new study from researchers at the University of Michigan C.S. Mott Children's Hospital's Child Health Evaluation and Research (CHEAR) Unit finds that using certain risk factors, including sexual history, to determine if a woman should be vaccinated could deprive more than 80 percent of eligible women from getting the vaccine.
What's more, the study - published in the Feb. 20 issue of Vaccine - reveals that such an approach would instead likely vaccinate a large number of women already infected with at least one of the four HPV strains the vaccination provides protection against, says study lead author Amanda F. Dempsey, M.D., Ph.D., MPH, a member of the CHEAR Unit team in the Division of General Pediatrics at C.S. Mott Children's Hospital.
"Selectively vaccinating women based on risk factors alone would mean that more than 2 million women, ages 18 to 26, who had the potential to derive the most benefit from HPV vaccination because they weren't already infected, would miss out on getting the vaccine," says Dempsey.
According to study results, behavioral risk factors should not be used by health care providers to determine if a young woman should be vaccinated. There were a lot of women in the study without certain risk factors that still had HPV, notes Dempsey.
Much of the confusion over whether or not to vaccinate a patient stems from conflicting vaccination recommendations. The American Cancer Society advocates vaccinating all females younger than 18, and selectively vaccinating women ages 19 to 26 based on an informed discussion between the patient and her doctor about sexual history. The Centers for Disease Control and Prevention's Advisory Committee on Immunizations Practices, however, recommends universal vaccination for all women ages 11 to 26, regardless of sexual experience.
Adding to that, the HPV vaccine is the most expensive routinely recommended vaccine. Financial barriers - underinsurance, no insurance, lack of state or federal vaccine financing - can make it difficult to provide the vaccine to all eligible females, says Dempsey.
Combined, these issues raise the question of whether or not a targeted approach to HPV vaccination among sexually active young women would be a better option than a comprehensive, universal vaccination strategy.
Using data from the National Longitudinal Study of Adolescent Health (Add Health), Dempsey and her colleagues worked to test the effectiveness of a targeted approach to vaccination. They evaluated how well certain risk factors correlate with having HPV, as well as what would happen if behavioral risk factors were used as a way to target the vaccine to only certain groups of women.
Among the study's 3,276 women, ages 19 to 24, more than 9 percent had at least one of the four HPV types that the vaccine protects against. When evaluated for all 27 HPV types, the prevalence of HPV infection grew to more than 26 percent among the study group.
Women with certain risk factors - an older sex partner, more than three lifetime sex partners, a new sex partner within the past year, and use of illegal drugs within the past year - were also more likely to have an HPV vaccine-type infection.
But the study reveals that using these risk factors to develop a clinical risk assessment tool for vaccine eligibility was not a viable vaccination strategy.
"As the number of behavioral risk factors increases, the likelihood that a woman is infected with at least one of the four types of HPV found in the HPV vaccine increases," says Dempsey. "However, no specific cutoff or threshold number of risk factors could be identified that would help a medical provider decide whether a person should or shouldn't get the vaccine. A sizeable proportion of women without each of the risk factors still had HPV."
As an example, Dempsey describes how using the risk factor of having had more than three lifetime sex partners would affect vaccination. In this case, 53 percent of women ages 18 to 26 would be vaccinated. but 47 percent of women without this risk factor would not. Of the unvaccinated group, 93.9 percent had no evidence of infection with any of the four HPV vaccine types - creating a missed opportunity to vaccinate women who could potentially derive the most benefit from the vaccine.
In addition to Dempsey, study co-authors are Achamyeleh Gebremariam, with the CHEAR Unit in the Department of Pediatrics at the U-M Health System; and from the Department of Epidemiology at the University of Washington, Laura A. Koutsky and Lisa Manhart.
The study was supported in part by the 2007 Ambulatory Pediatric Association Young Investigator Grant program.
Reference: Vaccine, Vol. 26, No. 8.
Written by Krista Hopson