A new study of human papillomavirus (HPV) in the U.S. suggests that the prevalence of the most concerning types of HPV has decreased significantly in female teenagers since introduction of the vaccine in 2006. Published in The Journal of Infectious Diseases, and now available online, the findings also suggest the vaccine is highly effective.
Approximately 79 million Americans are currently infected with HPV, and about 14 million people become newly infected each year, according to the Centers for Disease Control and Prevention (CDC). The most common sexually transmitted infection in the U.S., HPV can cause serious health problems, including genital warts and certain cancers, in women and men.
Two HPV vaccines are approved for use in the U.S. A quadrivalent vaccine that targets four different kinds of HPV (types 6, 11, 16, and 18) was introduced in 2006. A bivalent vaccine, approved in 2009, targets HPV types 16 and 18. Routine vaccination with three doses of either vaccine is currently recommended for females aged 11 or 12 and through age 26 if not vaccinated previously. (In 2011, routine vaccination of males aged 11 or 12 and through age 21, if not vaccinated previously, was also recommended in the U.S.) These four types of HPV cause 70 percent of cervical cancers and 90 percent of genital warts.
In this study, researchers at CDC analyzed changes in HPV prevalence over time, using the National Health and Nutrition Examination Surveys (NHANES). They compared HPV prevalence in females aged 14-59 years old before the start of the vaccination program (2003-2006) and the first four years after vaccine introduction (2007-2010). Researchers found that among those aged 14-19 years old in these two time periods, vaccine-type HPV prevalence decreased 56 percent, from 11.5 percent in 2003-2006 to 5.1 percent in 2007-2010. Other age groups did not show a statistically significant difference over time. Their research also showed that vaccine effectiveness for prevention of infection of at least one dose was an estimated 82 percent.
Reduction in vaccine-type HPV prevalence will be an important early measurement of the vaccine’s impact, the study authors noted. While HPV vaccine coverage continues to increase in the United States, a 2010 national immunization survey found that only 49 percent of 13- to 17-year-old female adolescents received at least one dose of the vaccine, and only 32 percent had received all three recommended doses.
The decline in vaccine type prevalence is higher than expected and could be due to factors such as to herd immunity, high effectiveness with less than a complete three-dose series and/or changes in sexual behavior not measured.
The decline in vaccine-type HPV prevalence suggested by the study findings “is encouraging, given the substantial health and economic burden of HPV-associated disease,” the study authors wrote. The study also provides “information to providers and public health policy makers on the impact of the vaccination program,” said lead study author Lauri E. Markowitz, MD. The researchers emphasized that they will continue to monitor the NHANES data for further HPV prevalence changes. “With continued monitoring, we can evaluate issues such as duration of protection,” Dr. Markowitz added.
Reduction in HPV prevalence among young women following vaccine introduction in the United States, National Health and Nutrition Examination Surveys, 2003-2010
http://jid.oxfordjournals.org/content/early/2013/06/18/infdis.jit192.full
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