SEATTLE – Vaccinating girls against human papillomavirus at age 11 or 12 years, as is currently recommended, appears to be most appropriate for preventing infection, but barriers persist, according to two studies presented at the annual meeting of the Society for Adolescent Health and Medicine.
In a study among girls as young as age 13 years, one in eight who reported that they had never had sexual intercourse nonetheless had vaginal infection with human papillomavirus (HPV). And more than two-thirds of those who had had sex were infected.
In another study among girls aged 14-17 years and their mothers, the most commonly cited reasons for not vaccinating were fear of side effects, perceived danger of the vaccine, and lack of a recommendation to vaccinate from their health care provider.
Prevalence of HPV infection. The Advisory Committee on Immunization Practices (ACIP) recommends that HPV vaccine be targeted to girls aged 11-12 years, with catch-up vaccination in girls and young women aged 13-26 years, noted Dr. Jessica A. Kahn, an associate professor of pediatrics at the University of Cincinnati.
But there is some reluctance among clinicians and parents alike to vaccinate at age 11 or 12, she said. "This is concerning, as HPV is commonly acquired during the teen years, and HPV vaccines are not effective at preventing infections with vaccine types of HPV in young women who are already infected with those types at the time of vaccination."
Data on the prevalence of type-specific HPV infection in girls initiating HPV vaccination are generally lacking, according to Dr. Kahn. "These data are needed in order to estimate the public health impact of HPV vaccination in the catch-up age group, and to guide educational and public health interventions designed to maximize the effectiveness of HPV vaccination."
She and her colleagues studied 259 girls aged 13-21 years who were receiving their first dose of HPV vaccine in a hospital-based adolescent clinic. Clinicians or the girls themselves collected vaginal samples that were tested for 37 HPV types. The girls and their mothers completed questionnaires about factors potentially related to HPV acquisition.
Overall, 27% of the girls were sexually inexperienced, reporting that they had never had vaginal or anal sex. But 13% of this group had had sexual contact, reporting genital skin-to-skin contact only.
The percentage of girls testing positive for any HPV type was 70% in the sexually experienced group and much lower, though not zero, at 12% in the sexually inexperienced group (P less than .001).
The sexually experienced group was also more likely than the inexperienced group to test positive for at least one of the high-risk HPV types in the quadrivalent vaccine – types 6, 11, 16, and 18 (31% vs. 4%, P less than .001) – and for at least one of those in the bivalent vaccine – types 16 and 18 (21% vs. 3%, P less than .001).
In a multivariate analysis of the sexually experienced group, these girls were significantly more likely to be HPV positive if they had had two to five, or six or more lifetime male partners, compared with one partner (odds ratios 6.2 and 10.3) and if their mother reported not having communicated with them about the HPV vaccine (OR 4.0).
In contrast, in the sexually inexperienced group, none of a variety of factors, including reported sexual contact, were independently associated with the odds of being HPV positive.
"Clinicians and parents should be strongly encouraged to vaccinate 11- to 12-year-old girls and not procrastinate," Dr. Kahn asserted. "It’s difficult to predict the age of sexual initiation, and thus, these recommendations by the ACIP minimize the probability that girls will be infected at the time of vaccination."
The findings also support the recommendation for catch-up vaccination in older girls, she added, as a majority of the sexually active group were still negative for high-risk types of the virus covered by the vaccines.
"I think it’s probably helpful for clinicians to develop some brief talking points for use with parents in terms of HPV vaccination," said Dr. Kahn. "Those would include the fact that HPV is acquired very rapidly after sexual initiation, that the vast majority of people will acquire HPV at some point in their lives, and that the vaccine is only effective in preventing vaccine-type HPVs if given before exposure."
"I think it’s really important for us to get those messages out, and I think it can be done in a pretty concise way," she concluded.
Barriers to HPV vaccination. Understanding barriers to HPV vaccination is important not only for promoting uptake, but also possibly for efforts to address disproportionately high rates of HPV infection in certain population groups, according to Dr. Laura M. Kester, a pediatrician at Indiana University in Indianapolis.