Predicting a child's future is a near impossible task - today's straight-A student may not become tomorrow's doctor, and the school-yard bully may actually grow up to become a member of the Peace Corps.
So why should an adolescent's sexual behavior- or lack thereof - determine whether or not she gets vaccinated against the human papillomavirus, to protect against future HPV infection? It shouldn't, say researchers at the University of Michigan C.S. Mott Children's Hospital's Child Health Evaluation and Research (CHEAR) Unit.
The study, set to appear in the July issue of the journal Pediatrics, finds women who were sexually active as adolescents were just as likely as women who were not sexually active during their youth to get HPV as adults.
"Using risk factors as a means to determine who should get the HPV vaccine is not a good strategy. In our study, all women who eventually became sexually active at some point had an equivalent risk of getting HPV," says study lead author Amanda F. Dempsey, M.D., Ph.D., MPH, a member of the CHEAR Unit in the U-M Division of General Pediatrics.
These findings, Dempsey says, support the Centers for Disease Control and Prevention's Advisory Committee on Immunizations Practices recommendation for universal vaccination for all women ages 11 to 26, regardless of sexual experience.
Much of the confusion over whether or not to vaccinate a patient stems from conflicting recommendations. While the ACIP advocates for universal vaccination, the American Cancer Society recommends 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 price of the vaccine is also a factor. With each dose costing approximately $120 - along with high up-front costs to stock the vaccine, inconsistent coverage from government programs and low levels of reimbursement from private insurance - many states are struggling to provide the vaccine to all eligible girls and women.
For those reasons, many clinicians are targeting the HPV catch-up vaccination to only girls and women they deem to be at the greatest risk for acquiring HPV. Previous studies of sexually active adolescents and young adults identified specific sexual partnerships, behavioral and sociodemogrpahic characteristics associated with increased risk for HPV infection.
The problem, Dempsey says, is that those studies only looked at women currently infected with HPV, and retrospectively analyzed potential risk factors for infection.
"Few studies have evaluated the ability of specific risk factors to predict future HPV infection prospectively," says Dempsey. "This is an important distinction, given that, to be effective, the HPV vaccine must be provided before vaccine type-specific infection occurs."
For their study, Dempsey and her colleagues selected six high-risk behaviors that have been shown in other studies to be associated for sexually active women with a higher risk of HPV - the number of sexual partners, history of having an older male sexual partners and/or a new sex partner with the past year, illegal drug use, history of sex while impaired by drinking, and regular use of cigarettes/alcohol. For virgins the team also assessed risk factors found in other studies to be associated with the acquisition of other sexually transmitted diseases, and early sexual activity.
Of the risk factors evaluated during adolescence, none were found to be associated with future HPV infection. Among sexually active adolescents, only a history of having sex while impaired by alcohol was associated with increased odds of testing positive for vaccine-type HPV as a young adult.
"Whether or not an adolescent was sexually active did not have an association with future HPV infection," says Dempsey. "Essentially all individuals who become sexually active are at risk for acquiring HPV, which is due to the high prevalence of HPV in society. So targeting particular groups for vaccination would prevent many at-risk women from being protected."
In fact, estimates suggest that more than 80 percent of the U.S. population will have had an HPV infection by the time they reach the age of 50.
The study also found:
- Of the 3,181 study participants, 43 percent reported being sexually active in the first wave of the study. The first wave included girls ages 11-17.
- Virgins with a history of illegal drug were at a decreased risk for young-adult HPV infection.
- Sexually active adolescents tended to be older, in a higher grade and were more likely to be African American.
- 53 percent of study participants, who tested positive for HPV in the third wave of the study (ages 18 and older), were virgins in the first wave of the study.
HPV infection generally occurs shortly after a woman becomes sexually active. Most women never know they have the virus because it usually goes away on its own and may not cause any symptoms. There are more than 100 types of HPV, but only some types of HPV lead to cervical cancer or genital warts. The vaccine guards against four types of HPV: two that cause 70 out of 100 cases of cervical cancer and two that cause 90 out of 100 cases of genital warts.
In addition to Dempsey, study co-authors were 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: Pediatrics, July 2008, Vol. 122, No. 1.