HPV Vaccine Produces Early Benefits for Teen Girls
Risk of precancerous changes dropped 44 percent several years after immunization
The researchers looked for cases of cervical dysplasia and genital warts in the girls because these tend to be the earliest signs of HPV infection, Smith said.
Cervical dysplasia is "not yet cancer, but over time, if it's left untreated and unchecked runs the risk of becoming cancer later in a girl's life," said senior author Linda Levesque, an assistant professor at the Queen's University Center for Health Services and Policy Research.
More than 2,400 cases of cervical dysplasia occurred in these girls between grades 10 to 12. However, the risk of cervical dysplasia was reduced by 44 percent in girls who received the vaccine, the study reports.
"This basically means that for every 175 girls who received the HPV vaccine, one fewer case of cervical dysplasia occurred," Smith said. "One case was prevented."
The researchers also found that girls eligible for free HPV vaccination ended up with fewer cases of genital warts, although the finding was not statistically significant.
"I don't think we were surprised the vaccine works," Levesque said. "What I was surprised by was the magnitude of benefits in such a young age group. I expected we would see some reductions. I didn't think they would be so large and of such significance."
Girls can receive the vaccine as young as 9, but health officials in the United States recommend the vaccine at 11 or 12, at the same time as other important adolescent vaccinations like tetanus/diphtheria/pertussis and meningitis, Saslow said.
This study involved the first HPV vaccine available on the United States and Canadian markets, Gardasil 4, which protects against four strains of human papillomavirus. Since then, two other vaccines -- Cervarix, which protects against two strains, and Gardasil 9, a new version of Gardasil that protects against nine strains -- have been approved in the United States.
Girls and boys both receive the HPV vaccine in a three-shot series within a six-month time frame.
Many parents and health care providers are hung up on the fact that the vaccine is for a sexually transmitted virus, and fail to grasp that it is the first vaccine to actually prevent cancer, Saslow said.