The rate of teenage Australian girls showing early signs of cervical cancer fell nearly in half following the start of a national program to vaccinate women against the human papilloma virus, a new study shows.
The study is the first to demonstrate that a vaccine program can lower the rate of precancerous cervical lesions in a population.
Australia's HPV vaccine program began in April 2007.
The result is not surprising, said Dr. Maura Gillison of Ohio State University, who studies the role of HPV in cancer and was not involved in the Australian study.
"In clinical trials, the HPV vaccines were demonstrated to be extraordinarily effective in preventing the development of cervical pre-cancers caused by HPV 16 and 18," said Gillison, referring to the two viral strains believed to lead to cervical cancer. "This study demonstrates for the first time the extraordinary benefit to a population of young women of a public health policy that rapidly incorporated an anti-cancer vaccine into its state-supported vaccine program."
The vaccine also has been available in the United States since 2006, but Gillison said fewer U.S. women get vaccinated, making a similar drop in cases of precancerous lesions unlikely.
The results of the new study are published online today in the journal The Lancet.
The Australian study
The researchers, led by Dr. Julia Brotherton of the Victorian Cytology Service Registries in East Melbourne, used data in a national registry of pap test results. (The pap test, done during gynecological exams, detects the presence of HPV in cervical cells.)
Before the vaccination program, eight out of every 1,000 girls younger than 18 were found to have "high-grade cervical abnormalities." After the program began, that rate fell to 4.2 girls per 1,000.
The researchers also analyzed data for women over 18 but did not find any drop. Women over 18 were more likely to have had previous sexual experience and thus less likely to benefit from the vaccine, the study said.
The findings reinforce the idea that the vaccine should be given to younger girls, the researchers said.
Differences in the U.S.
While the findings might be an early sign of the "real-life effect" of the vaccine, the results should be viewed with caution, wrote Dr. Mona Saraiya and Susan Hariri of the U.S. Centers for Disease Control and Prevention in an editorial accompanying the study.
Considering the dramatic decrease seen in girls under 18, "a similar though smaller decrease would be expected in girls in the next oldest age group," because many in this age group were vaccinated and they, too, were likely to benefit from the vaccine. However, the study did not find such a decrease.
"The not-so-cautious optimist in us wants to hail this early finding as true evidence of vaccine effect," Saraiya and Hariri wrote. But the study did not look at analyze the findings on an individual level? for example, they did not look at whether those with cervical lesions had been vaccinated ? so further analysis is needed.
In Australia, about 80 percent of girls ages 12 to 13 have received the HPV vaccine since 2007, Gillison said. In the U.S, the vaccination rate of this age group has only recently risen to a peak just above 30 percent.
A previous study from Australia showed reductions in the incidence of genital warts (caused by two other strains of HPV that the vaccine also protects against) after introduction of the HPV vaccine, Gillison said.
Pass it on: Fewer girls in Australia are developing early signs of cervical cancer since the country's national vaccine program began.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.