HPV Vaccine Appears Responsible for Dramatic Drop in Infections

Just a third of teenage girls have received the recommended 3-dose course of the HPV vaccine, but a new study finds that infections have dropped by more than half since the vaccine was introduced.

Human papillomavirus (HPV) infections in teen girls aged 14 to 19 have dramatically decreased since the introduction of the HPV vaccine in 2006 despite low coverage rates, finds a study published online on June 26, 2013, in the Journal of Infectious Diseases.

For the study, researchers at the Centers for Disease Control and Prevention (CDC) analyzed data on HPV prevalence from National Health and Nutrition Examination Surveys conducted before (2003 to 2006) and after (2007 to 2010) the vaccine was made available. Just 4 years after the introduction of the vaccine, the researchers found a 56% reduction in the prevalence among girls aged 14 to 19 of the types of HPV infection covered by the vaccine, which commonly cause genital warts and cervical cancer. From 2003 to 2006, overall vaccine-type HPV prevalence in this group was approximately 11.5%, dropping to just 5.1% from 2007 to 2010.

The vaccine was estimated to be 82% effective in preventing HPV when patients received at least 1 of the recommended 3 doses. The researchers found no significant decrease in HPV infections in other age groups, most likely because the vaccine is not recommended for women over the age of 26 and is primarily targeted toward adolescents.

The researchers also report that HPV infection rates did not show significant changes before the vaccine was introduced, leading them to believe that the vaccine is the main cause for the reduction. To further test this theory, the researchers analyzed measures of sexual behavior during both study periods and found no difference in either the number of teenagers having sex or their number of sexual partners.

The extent of HPV reduction found by the study is surprising considering that only about one-third of girls aged 14 to 19 have received the recommended 3-dose vaccination course. However, approximately half have received at least 1 dose of the vaccine, which appears to have contributed to the decrease in HPV infections. As lead study author Lauri E. Markowitz, MD, a medical epidemiologist with the CDC, explained in a telephone briefing on the study, those teenagers who did receive the vaccine reduced the virus’s spread, helping provide “herd immunity” to others who had not received it. It is also possible that those who got the vaccine were more sexually active on average and would have been more likely to spread the virus if unvaccinated. More research is needed, however, to fully understand how the vaccine has led to such a dramatic drop in HPV infection rates.

The researchers also hope to increase the number of teenagers who receive the HPV vaccine. An estimated 53,000 cases of cervical cancer could be prevented throughout the lives of girls currently aged 13 and younger if vaccination rates in the United States increased to 80%. However, the vaccine continues to face resistance from those who have safety concerns or believe that it encourages sexual activity among teenagers. As a result, the United States has not yet joined the ranks of other nations, including the United Kingdom, Australia, Denmark, and Rwanda, which have reached at least 70% coverage levels.

CDC Director Tom Frieden, MD, MPH, is adamant that the vaccine is safe, has not been shown to increase risky sexual behavior in teens, and is necessary to prevent cervical cancer. “The bottom line is this—it's possible to protect the generations from cancer, and we've got to do it,” Dr. Frieden said in the telephone press briefing.

Two HPV vaccines are currently available—Gardasil and Cervarix—and a 3-dose course of either is recommended for all females aged 11 to 26. Vaccination with Gardasil is also recommended for males aged 11 through 21.