Pharmaceutical company Merck on Thursday at a meeting of the European Society of Pediatric Infectious Diseases in Valencia, Spain, announced that a study of the company's experimental vaccine targeting the four strains of the sexually transmitted disease human papillomavirus that are most likely to cause cervical cancer or genital warts showed that the vaccine produces a stronger immune response in male and female adolescents ages 10 to 15 than in young women ages 16 to 23, Reuters reports. The Phase III trial involved 1,529 people who received a three-dose regimen of the vaccine -- known as Gardasil -- over a six-month period. The study found that males and females ages 10 to 15 produced a higher level of antiviral antibodies to HPV than women ages 16 to 23 (Reuters, 5/20). Among 10- to 15-year-old girls and boys, 99.9% of participants developed antibody responses to HPV strain 18, compared with 99.1% among 16- to 23-year-old women, according to the study (AP/Yahoo! News, 5/19). All participants experienced 100% antibody responses to the other three HPV strains -- types 6, 11 and 16 (Merck release, 5/19). Antibody levels for all four types of HPV were significantly higher among the adolescent boys and girls than among women in the older age group, the AP/Yahoo! News reports. An estimated 20 million U.S. residents are infected with HPV, which causes most cases of cervical cancer, according to Merck (AP/Yahoo! News, 5/19). About 250,000 women worldwide die annually from cervical cancer, and the American Cancer Society estimates that about 3,700 women die of the disease each year in the United States.

Vaccinations for Adolescents
The study results could help "pave the way" for Merck to receive a federal recommendation to conduct routine HPV vaccinations among young people, the Wall Street Journal reports (Martinez, Wall Street Journal, 5/20). Merck might try to convince states to require the vaccine for all 12-year-old children before they can enter school, and GlaxoSmithKline plans to recommend its HPV vaccine for girls as young as age 10. However, some parents and health officials object to standardized vaccinations for teenagers and are concerned that children would interpret them as permission to have sex (Kaiser Daily Reproductive Health Report, 4/5). The vaccine is most effective before an individual becomes sexually active, which is why Merck sees its target population as women ages nine to 24, according to the Journal. However, Merck "will have to navigate tricky waters" to obtain the recommendation and might face "political concerns that the vaccine reduces the health risks of sex for young people," the Journal reports (Wall Street Journal, 5/20).

Comments
"Not only did this study demonstrate vaccine-induced immune responses are higher among young adolescents compared to young adult women, this analysis is also the first time we've been able to assess antiviral responses in adolescent males," Terry Nolan -- a lead researcher in the study and a professor in the School of Population Health and director of the Department of Public Health at the University of Melbourne -- said, adding, "It is important to consider the role of both sexes when talking about the public health impact of HPV" (Merck release, 5/19). Eliav Barr, director of clinical research for HPV vaccines at Merck, said the study is the first to examine adolescents' response to an HPV vaccine. "What it means is that both kids as well as adults over the entire age range almost all respond to the vaccine," Barr said (Reuters, 5/20).

Other Studies, Approval
Merck said it expects to release data from other Phase III trials on Gardasil -- involving about 25,000 participants worldwide -- later this year, the AP/Yahoo! News reports (AP/Yahoo! News, 5/19). A study of the Phase II trials published in the April issue of the journal Lancet Oncology showed that Merck's vaccine was 89% effective at preventing infection with the four HPV strains and 100% effective at preventing cervical cancer, precancerous lesions or genital warts. Luisa Villa, a biologist at the Ludwig Institute for Cancer Research in Sao Paulo, Brazil, and colleagues conducted the Phase II trial of the vaccine among 552 women ages 16 to 23 in the United States, Europe and Brazil. GSK is testing its vaccine in thousands of women around the world to confirm the effectiveness and safety of the vaccines. Separate studies testing the effectiveness of Merck's and GSK's vaccine targeting HPV strains 16 and 18 have shown similar results. Currently, the companies are competing to get their products approved. GSK plans to file for regulatory approval for its vaccine, called Cervarix, in Europe in 2006. Merck plans to apply for FDA approval for its expanded HPV vaccine later this year (Kaiser Daily Reproductive Health Report, 4/8).