July 9, 2012 -- The vaccine against the human papilloma virus (HPV) is not only effective in decreasing the rate of high risk types of HPV infections in girls and women, but it also shows evidence of bestowing what is known as "herd immunity" -- an indirect protection against the virus for those who have not been vaccinated -- in a community at large, researchers said Monday.
Researchers at the Cincinnati Children's Hospital Medical Center compared HPV infection rates in women who received the HPV vaccine to infection rates in those who had not.
What they found was that women who received the HPV vaccine cut their likelihood of having an HPV infection by 69 percent. The surprise was that the likelihood of HPV infection among women in the same community who had not gotten their HPV shots also dropped -- by 49 percent.
"I was surprised at the decrease in the prevalence of HPV and the effectiveness of the vaccine in a real-world setting," said Dr. Jessica Kahn, lead author of the study, which appeared Monday in the journal Pediatrics.
But Kahn said that while the finding was encouraging, it should not deter parents from getting their children vaccinated.
"Although the study shows evidence of early herd immunity, the results cannot be generalized to imply you shouldn't get vaccinated," she said. Kahn said it is "still very important... there is no way of knowing you are one of those protected unless you actually get the vaccine."
Other experts in infectious diseases agreed that the study demonstrates how important it is to get vaccinated.
"I think it is important to point out to potential vaccine recipients that herd immunity is routinely achieved when greater than 80 percent of the population has been vaccinated," said Robert Rose, professor emeritus of infectious diseases at the University of Rochester in Rochester, N.Y. "Thus, it is incumbent upon immune-competent individuals to participate in the vaccine effort in order to protect those who are in one way or another immune-compromised."
HPV is responsible for the most common sexually transmitted infections. There are more than 100 types of HPV, including more than 40 high-risk types of infection that are responsible for causing approximately 70 percent of cervical cancers, genital warts, vaginal and anal cancers and a growing number of head and neck cancers, especially in men.
Since these viruses have the ability to cause such widespread disease, current recommendations from the U.S. Advisory Committee on Immunization Practices include vaccination against HPV for both males and females ages 9 to 26.
"Substantially decreasing the incidence of this disease by using a preventive vaccine is so exciting, especially when approximately 20 percent of human cancers are caused by an infection," said Dr. Connie Trimble, an OB/Gyn and HPV researcher at Johns Hopkins University in Baltimore, Md.
Despite the growing body of research supporting HPV vaccination, however, HPV vaccination rates among young people remain low. According to the U.S. Centers for Disease Control and Prevention, rates were only around 49 percent for the first out of three required doses. Additionally, while the current HPV vaccine shows effectiveness in reducing the prevalence of the four most high-risk types of infection in Kahn's study, other types of HPV remain prevalent.
Dr. James Turner, member of the Vaccine Preventable Disease Committee at the University of Virginia, said there remains a need to continue to improve and change the vaccine in a way that acts against the types of the virus that remain prevalent in the community.
"I believe manufacturers are in Phase II studies of developing new vaccines that cover up to nine [types] of HPV, which if effective, will really enhance protection against HPV," he said.