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Lower HPV Prevalence Among Young Women Credited to Vaccine

The prevalence of human papillomavirus (HPV) among teenage women in the U.S. has declined substantially in recent years -- falling by more than 50% -- coinciding with widespread HPV immunization starting in 2006, according to a CDC study described in the June 19, 2013, advance edition of the Journal of Infectious Diseases.

HPV can trigger abnormal cell growth ranging from warts to dysplasia to invasive cancer. HPV types 16 and 18 are responsible for most cases of cervical and anal cancer, and recent research has also linked some mouth and throat cancers to the virus.

Most people become infected with HPV soon after they become sexually active, so vaccination is recommended before this occurs. In late 2006 HPV vaccination was added as a routine immunization in the U.S. for girls age 11-12 years, with "catch-up" vaccination recommended for young women up to age 26. Vaccination is now recommended for boys and young men as well.

The most widely used vaccine, Merck's Gardasil, prevents infection with HPV types 6 and 11 (which cause genital warts), 16, and 18. GlaxoSmithKline's Cervarix only protects against 16 and 18. In 2010, an estimated 32% of 13-17 year-old women had received all 3 doses of the vaccine series, the study authors noted as background; about half had received a single dose, which confers partial protection.

Using data from the large National Health and Nutrition Examination Survey (NHANES), Lauri Markowitz from the U.S. Centers for Diseases Control and Prevention and colleaguescompared prevalence of HPV among women during the pre-vaccine era (2003-2006) versus the vaccine era (2007-2010). More than 4000 women age 14 to 59 provided cervical-vaginal swab samples during each period.

Results

• Among women of all ages combined, HPV prevalence did not differ significantly between the 2 time periods: 42.5% during 2003-2006 vs 39.8% during 2007-2010.
• Among young women age 14-19 years, however, prevalence of any HPV infection fell from 32.9% to 26.1%, which did reach statistical significance.
• Looking atthe 4 HPV types in the vaccine, prevalence fell from 11.5% during 2003-2006 to 5.1% during 2007-2010 -- a decline of 56%.
• Looking just at the "high-risk" or cancer-causing types 16 and 18, prevalence fell from 7.2% to 3.6%, also a significant drop.
• Interestingly, the prevalence of some other high-risk strains not included in the vaccine also fell, from 20.7% to 16.4%.
• The estimated effectiveness of at least 1 dose of the vaccine was 82%.

"Within 4 years of vaccine introduction, the vaccine-type HPV prevalence decreased among females aged 14-19 years despite low vaccine uptake," the researchers concluded.

"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 3-dose series and/or changes in sexual behavior we could not measure," Markowitz explained in a press released issued by the CDC.

Although HPV prevalence did not differ significantly between the 2 time periods for other age groups, the benefit of vaccination is expected to extend to older women -- as well as boys and men -- with prolonged duration of vaccine coverage.

"This report shows that HPV vaccine works well, and the report should be a wake-up call to our nation to protect the next generation by increasing HPV vaccination rates," said CDC director Thomas Frieden. "Unfortunately only one third of girls aged 13-17 have been fully vaccinated with HPV vaccine," he added, compared with more than 80% in Rwanda.

The HPV vaccine is more expensive in the U.S. than in low-income countries, and it took some time after its introduction before it started to be widely covered by insurance. The vaccine remains controversial among some parents, who fear the vaccine could encourage or send a message condoning early sexual activity.

"Our low vaccination rates represent 50,000 preventable tragedies -- 50,000 girls alive today will develop cervical cancer over their lifetime that would have been prevented if we reach 80% vaccination rates," Frieden noted. "For every year we delay in doing so, another 4,400 girls will develop cervical cancer in their lifetimes."

6/21/13

Reference

LE Markowitz, S Hariri, C Lin, et al. Reduction in Human Papillomavirus (HPV) Prevalence Among Young Women Following HPV Vaccine Introduction in the United States, National Health and Nutrition Examination Surveys, 2003-2010. Journal of Infectious Diseases. June 19, 2013 (Epub ahead of print).

Other Sources

Centers for Diseases Control and Prevention. New Study Shows HPV Vaccine Helping Lower HPV Infection Rates in Teen Girls. Press release. June 19, 2013.

Centers for Diseases Control and Prevention. CDC Telebriefing on HPV prevalence among young women following HPV vaccination introduction in the United States, NHANES, 2003-2010. Telebriefing transcript. June 19, 2013.