June 17, 2011 -- Health officials in Australia are reporting what may prove to be the first evidence that the vaccine targeting the human papillomavirus (HPV) could prevent cervical cancer in a large population.
Between 2007 and 2009 -- the first three years of the program -- high-grade cervical abnormalities declined by 50% in Victoria, Australia, among girls aged 17 and younger.
Vaccine Effect? ‘Too Soon to Say’
Australia was the first country to implement population-wide HPV vaccination targeting girls in their teens and early 20s, with the goal of vaccinating all girls as they enter high school at age 12 or 13. A "catch-up" program also targets older teens and women in their early 20s.
Researchers are still working to determine if the decline in precancerous lesions among teen girls was limited to those who had been vaccinated, so it is too soon to say if it represents true evidence of a vaccine effect, epidemiologist Julia M. Brotherton, MD, MPH, tells WebMD.
“It certainly looks like this could be a vaccine effect, but until we are actually able to link vaccine registry data with Pap test data we can only speculate about that,” she says. “What we can say is that this is an exciting, early finding.”
HPV Causes Most Cervical Cancers
Human papillomavirus (HPV) is the major cause of cervical cancer, which kills about 4,000 women in the United States each year.
The sexually transmitted virus is very common, and that is why most vaccine programs target young girls who are not yet sexually active. Since the first HPV vaccine was licensed in 2006, many countries, including the U.S., have included it in their recommended immunizations. But Australia’s program is one of the few that includes school-based vaccination and screening of teens for HPV-associated cervical abnormalities.
In the new study, published in the June 18 Lancet, Brotherton and colleagues report that the incidence of high-grade abnormalities found on Pap tests fell nearly 50% from nearly one in 100 girls under age 18 pre-vaccination to one in 200 girls post-vaccination.
Similar declines were not seen in older teens and young women, suggesting that targeting girls before they become sexually active is critical, Brotherton says.
Just 27% of U.S. Teens Fully Vaccinated
Australia’s school-based vaccination approach has led to greater coverage of young girls than in most other countries.
In 2009, about 72% of Australian girls in their mid teens had had the three recommended doses of the HPV vaccine, compared to just under 27% of American teens, says epidemiologist Mona Saraiya, MD, MPH, of the CDC’s Division of Cancer Prevention and Control.
But another aspect of Australia’s program -- screening teens for cancerous or precancerous lesions -- remains controversial.
The American Congress of Obstetricians and Gynecologists recommends cervical cancer screening begin at age 21, and in many European countries screening is not recommended until age 25.
In Australia, screening begins at age 18, which could potentially lead to unnecessary and potentially harmful treatment to destroy high-grade cervical lesions, Saraiya says.
Cervical cancer is rare in very young women, and most women with genital HPV clear the infection on their own without treatment, which is why many medical organizations recommend against screening before age 21.
In an editorial also appearing in The Lancet, Saraiya writes that conclusive evidence that the HPV vaccine reduces cervical cancers will take several decades.
“The not-so-cautious optimist in us wants to hail this early finding as true evidence of vaccine effect,” she writes, adding that studies under way should increase understanding of the vaccine’s effectiveness against cervical disease.