The human papillomavirus (HPV) vaccine has slashed rates of the HPV strains covered by the vaccine by more than half in teens and by a third among women in their 20s, found a new study—and that’s before the newest vaccine with greater coverage of HPV strains had even been introduced. HPV causes nearly all cervical cancers as well as a proportion of oral, vulvar, vaginal, penile and anal cancers.
“Women in their teens and twenties are most at risk for these infections, so vaccination is protecting this target population,” said Kevin Ault, MD, FACOG, a professor of obstetrics and gynecology at the University of Kansas Medical Center. Though not involved in this study, Ault’s research focuses on the HPV vaccine and HPV detection. “This is an American study, but you can find similar data from Denmark, Australia and other countries,” he added.
In the study, a team of CDC researchers led by Lauri Markowitz, MD, compared the prevalence of HPV infections in girls and women, ages 14 to 34, before and after the vaccine’s introduction. They used data from an ongoing national survey which also collected cervical-vaginal samples swabbed from the female participants. These samples were analyzed for the DNA of HPV-6, -11, -16 and -18, the four types covered by the quadrivalent vaccine Gardasil, manufactured by
The researchers compared samples collected from 2,587 females between 2003 and 2006—before the vaccine had been recommended—to samples collected from 2,061 females between 2009 and 2012. Among the latter group, about half the girls ages 14-19 and a third of the women ages 20-24 had received at least one dose of the vaccine.
Among the teens, the prevalence of any of the four strains of HPV tested dropped from 11.5% before the vaccine to 4.3% after the vaccine, a reduction of 64%. The rate of HPV infections from HPV-16 and HPV-18, the two strains responsible for the lion’s share of cervical cancer, dropped from 7.1% before the vaccine to 2.8% after its introduction.
Among women in their early 20s, the rate of the covered four HPV strains dropped from 18.5% to 12.1%, and the combined rate of HPV-16 and HPV-18 dropped from 15.2% to 10.5%. Women age 25 and older did not show any differences in their rates of infection for any HPV strains.
The researchers also tested the prevalence of eight strains not covered by the vaccine, including the five that have since been added to the newest vaccine, and found no significant differences in rates between the pre-vaccine and post-vaccine time periods. That indicates that the drop in the other four strains is due to the vaccine.
When the researchers looked only at those who had been vaccinated, they found that overall rates of HPV of any strain weren’t much different before and after the vaccine—but there was a huge drop in infections caused by the four strains covered by the vaccine. The rate of HPV-6, -11, -16 and -18 infections dropped from 18.6% before the vaccine to 2.1% among those in 2009-2012 who had been vaccinated. Yet the rate was 16.9% among those in 2009-2012 who did not get the vaccine.
The reduction in HPV infections also did not occur due to changes in sexual behaviors. The proportion of females who reported ever having sex or having sex within the past year and the number of lifetime partners reported by the respondents did not differ between the two time periods—with one exception. More women ages 20 to 24 reported in 2009-2012 that they had had at least two partners in the past year and at least three lifetime partners, compared to women in 2003-2006. If anything, then, with more sexual partners, the rate of HPV infections would have increased if not for the vaccine.
The CDC recommends that all girls and boys receive three doses of the HPV vaccine starting around age 11, though the Advisory Committee on Immunization Practices will be examining evidence on Wednesday regarding the effectiveness of two-dose regimes. The CDC also recently added the HPV-9 vaccine to the recommended immunization schedule as an option in addition to the four-strain vaccine.
“The HPV 9-valent vaccine should make a significant impact on HPV infection, abnormal pap smears and treatment for pre-cancerous diseases of vulva, vagina and cervix,” Ault said. “Approximately 25% of cervical cancer is due to the ‘extra’ HPV types in the new HPV 9 vaccine.”
He added that the number of studies bearing “good news” about the safety and effectiveness of HPV vaccines has been increasing, even as doctors are among the biggest obstacles to more widespread vaccination. “Doctors need to emphasize that there are 27,000 HPV-related cancers in the U.S. every year, and it has become clear that this vaccine will help decrease that number,” Ault said.
Cervical cancer screenings continue to an important way to reduce cancer by catching pre-cancerous cervical dysplasia before it developed into cancer, but the HPV vaccine can prevent the infections that lead to dysplasia in the first place. Reductions in cancer from the vaccine will not be seen in the research for a while still because the vaccine has only been available for about 10 years.
“HPV infection is a necessary step on the path to cervical cancer, as well as a few other cancers,” Ault said. “This process has a long lag time, probably one or two decades. There are several studies from other countries that show the cervical dysplasia is decreased from the vaccine.”
These findings of this study, published in the journal Pediatrics, come in the wake of a recent presentation at the annual meeting of the American Association for the Advancement of Science related to increasing rates of HPV and related cancers, particularly among middle-aged white men. Due to the increase in HPV infections alongside the decrease in smoking, approximately 70% to 80% of oropharyngeal cancers are now caused by HPV, explained Gypsyamber D'Souza, PhD, an associate professor of cancer epidemiology at Johns Hopkins University Bloomberg School of Public Health.
More than 90% of these HPV-related head and neck cancers are caused by HPV-16, one of the strains in both Gardasil and Cervarix vaccines. Although each person’s overall lifetime risk of developing HPV-related oropharyngeal cancer is about 1.1%, there are approximately 45,780 new cases each year—and one person dies from this cancer every hour. But not everyone’s risk is equal: white men in their 50s were at the highest risk, and their cancer developed from HPV infections perhaps a decade earlier, underscoring the importance of the HPV vaccine in males as well.
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