In the decade since the HPV vaccine was introduced, it has substantially reduced cervical pre-cancers, genital warts and abnormal Pap smears in countries with immunization programs, according to a new international review.
The review, published online this month in the journal Clinical Infectious Diseases, looked at 58 studies of the effectiveness of Merck's Gardasil vaccine in Australia, Europe, North America, and New Zealand. The review was funded in part by a Merck-supported healthcare research company.
Gardasil protects against sexually transmitted strains of the human papillomavirus (HPV) that cause most genital warts and 70 percent of cervical cancers, as well as some less common cancers of the head, neck, and genitals that occur in both men and women. (A newer version of Gardasil protects against strains that cause 90 percent of cervical cancers.)
Because HPV-related cancer typically takes decades to develop, the full impact of the vaccine will take more time to emerge.
But the early impacts are clear, especially among girls, the review found. Declines in genital warts were observed just a year after the vaccine was introduced in Australia and Germany. All nine countries with effectiveness studies saw reductions in genital warts of up to 90 percent over the decade.
Vaccination also reduced cervical pre-cancers -- which are found through Pap testing and treated surgically to prevent progression to cervical cancer -- by as much as 85 percent. Less severe cervical abnormalities decreased by as much as 45 percent.
"The impact of the vaccine in real-world settings has become increasingly documented and is attributable to high vaccine effectiveness in targeted populations with high coverage," wrote the researchers, led by Suzanne M. Garland of the Royal Women's Hospital in Victoria, Australia.
The vaccine, given in three shots over six months, is recommended for girls and boys 11 and 12, so they can be protected before they become sexually active. In the U.S., federal data show that among 13- to 17-year-olds, only 37 percent of girls and 13 percent of boys have gotten all three shots. Doctors and parents of adolescents remain disconcerted by the vaccine's novelty, complexity, and link to sexual activity.
"Disappointingly, preventable HPV-related diseases persist," the researchers wrote, "underscoring the need for wide-reaching HPV vaccination programs."
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