A new study shows that the vaccine against the types of human papillomavirus—or HPV—that commonly cause cervical cancer in women has dropped by half since the vaccine was introduced in 2006.
The study, published Wednesday in the Journal of Infectious Diseases, looked at the prevalence of HPV infections in girls and women before and after the introduction of the HPV vaccine. It found that since the vaccine was introduced in 2006, the prevalence of HPV that the vaccine protects against has dropped 56 percent among women ages 14 to 19.
"These are striking results," said Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, during a phone call with reporters Wednesday. "And I think they should be a wake-up call that we need to increase vaccination rates because we can protect the next generation of adolescents and girls against cancer caused by HPV. The bottom line is this—it's possible to protect the generations from cancer, and we've got to do it."
Some strains of HPV, the most common sexually transmitted disease, is linked to cervical cancer, cancers of genitalia in men and women, and cancers of the head and neck, also in men and women.
The development of a vaccine prompted some states to require it for school admission, but an initial flurry of activity has died down, according to the National Conference of State Legislatures. While many laws have been proposed requiring the vaccine for teen girls, and boys, for whom the CDC also recommends it, the District of Columbia and Virgina remain the only state-level entities to require it, although Texas did for a time, too. (An executive order by Republican Gov. Rick Perry would have required the vaccine for girls to enter school, but the Texas legislature overturned it before it could take effect.)
The vaccine can be most effective when it is administered before children become sexually active. But many parents object to mandating the vaccine, especially for girls as young as 12, because they worry that the protective measure will make their children more cavalier about having sex, and earlier than they might have otherwise.
But Frieden said the study also found that there was no change in teenagers' sexual practices or sexual risks over the course of the eight years before and after the HPV vaccine was introduced. He compared the HPV vaccines to any other childhood inoculation.
"In terms of waiting until teens are sexually active, I think this really misses the point," he said. "We vaccinate well before people are exposed to an infection. We vaccinate for measles, for example, early in childhood or infancy, age 1, because that's well before a child may get exposed. Similarly, we want to vaccinate children well before they may get exposed."
Some parents have also hesitated about the vaccine because they are concerned about its safety.
The study noted 42 reports of deaths following vaccination, said Dr. Cindy Weinbaum, from the CDC's immunization safety office, but the causes of death were very different. "There's no consistent pattern among the deaths that have occurred to people following when they've been vaccinated by the HPV vaccine to give us concern that these deaths might be at all related."
Frieden said about 79 million Americans are infected with HPV, and about 14 million Americans become newly infected every year, but only a third of 13- to 17-year-old girls in the U.S. has received all three parts of the HPV vaccine. The doses must be spread over about a six-month period.
"Countries including Rwanda have vaccinated a higher percentage of females in the target population than we have in the U.S.," Frieden said. "Our low vaccination rates represent 50,000 preventable tragedies—50,000 girls alive today will develop cervical cancer that would have been prevented if we had reached our goal of 87 percent vaccination rates. In fact, for every single year we delay in reaching that rate, another 4,400 women will develop cervical cancer despite good screening."