JACKSONVILLE, FLA. — Universal immunization of preteenage girls with human papillomavirus vaccine would be ideal given the peak prevalence rates among adolescents in the United States, according to a presentation at an STD prevention conference sponsored by the Centers for Disease Control and Prevention.
“For the vaccine to have an optimal effect, it should be given before initiation of sexual behavior,” said Cristen Suhr, project coordinator of the HPV sentinel surveillance project sponsored by the CDC. [Since this meeting the CDC Advisory Committee on Immunization Practices recommended that the human papillomavirus vaccine should be given to all girls at age 11–12, and to all females aged 13–26 who have not been previously vaccinated. The vaccine can be given to girls as young as 9 years of age, at the provider's discretion (PEDIATRIC NEWS, July 2006, p. 1).]
A high overall prevalence of high-risk human papillomavirus (HR-HPV) infection, 22%—regardless of race—is among findings of the surveillance project. HR-HPV is defined as HPV strains 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, and 68.
The prevalence of HR-HPV in 14- to 19-year-olds is 33%. The project is the first multisite surveillance to measure HR-HPV prevalence among U.S. women.
Researchers assessed 8,426 females aged 14–65 years. Participants had a routine Pap smear between January 2003 and December 2005 in one of six cities: Baltimore, Boston, Denver, Los Angeles, New Orleans, or Seattle. Medical records were later abstracted for results.
Although nearly 60% of participants fell into the two youngest age groups (14- to 19-year-olds and 20- to 29-year-olds), “a strength of the ongoing HPV Sentinel Surveillance is inclusion of older age groups,” said Ms. Suhr. “Older women were more likely to be enrolled through a primary care clinic, whereas younger women were more likely to be enrolled through a family planning or STD clinic.”
“There was a steady decline in prevalence as age increased, from more than 30% in 14- to 19-year-olds down to under 10% in 50- to 65-year-olds,” Ms. Suhr said. This higher prevalence among younger females supports other studies that suggest HPV infection is acquired shortly after initiation of sexual activity. Ms. Suhr is affiliated with the CDC Division of STD Prevention and with Business Computer Applications Inc. in Atlanta.
HPV is the most common sexually transmitted infection, with a prevalence estimated at 20 million cases in the United States. Approximately 5.5 million incident infections occur each year. The HPV family is large, with more than 100 viral types, including more than 40 that cause genital infections. Most new infections are asymptomatic and clear naturally, but those that persist can cause cervical lesions.
The quadrivalent vaccine (Gardasil, Merck & Co.) targets high-risk oncogenic virus types 16 and 18, implicated in 70% of cervical cancers, as well as low-risk, nononcogenic types 6 and 11, which cause 90% of genital warts. Licensure of an investigational HPV bivalent vaccine (Cervarix, GlaxoSmithKline) is expected as early as the end of 2006.
“In the U.S., it appears we will be able to reduce abnormal Pap smears with the vaccines,” Dr. Diane M. Harper said. “We know the vaccines are safe [and] immunogenic and can prevent HPV infections—incident and persistent—and prevent genital warts.” Dr. Harper is director of the Gynecologic Cancer Prevention Research Group at the Norris Cotton Cancer Center in Lebanon, N.H.
“Surveys indicate a high level of acceptability of this vaccine among adolescents, young adults, parents, and providers. But there are also concerns about increases in risky behavior with this vaccine,” Dr. Judith N. Wasserheit, professor of allergy and infectious diseases, University of Washington, Seattle, said in another presentation at the meeting. The median age of first coitus in the United States is 16–17 years, she reported. One-third of adolescents initiate coitus by ninth grade, and 10% of ninth graders report a history of more than four partners.
Another area of controversy is school immunization requirements. These requirements are critical to ensuring coverage for young people, especially for higher-risk youth who may have limited access to health care, Dr. Wasserheit said. “Some argue that HPV is not transmitted in schools, so why should it be required? But this is an access point. We may not get to school requirement in the first round with this vaccine, but it's important.”
Potential limitations of the study include its clinic-based population and use of noncentralized laboratories for testing of cervical fluid samples.
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