Healthday News — Human papillomavirus (HPV) prevalence among young women has declined by more than half since the introduction of a three-dose vaccine in 2006, CDC data indicate.
Among young women aged 14 to 19 years, HPV strains included in the vaccine decreased 56% in the four years after the vaccine became available despite the fact that only one-third of eligible patients received the vaccine, Lauri E. Markowtiz, MD, and colleagues reported in the Journal of Infectious Diseases.
“The decline in vaccine type prevalence is higher than expected and could be due to herd immunity from vaccination, vaccine effectiveness of a series involving <3 doses, and/or changes in sexual behavior that we did not measure,” the researchers wrote.
The FDA approved the first quadrivalent HPV vaccine (Gardasil, Merck) in 2006, which offered protection against the four viral strains most closely associated with gynecologic cancer — HPV types 6, 11, 16 and 18.
In June of that year the ACIP recommended routine vaccination of 11- and 12-year-old girls with three doses of the quadrivalent vaccine, and catch-up vaccination for girls and young women aged 13 through 26.
An additional bivalent HPV vaccine (Cervarix, GlaxoSmithKline) with protection against HPV types 16 and 18 was approved and recommended by the ACIP in 2009. As of 2011, the committee recommended routine HPV vaccination of boys and young men, but they were not included in this study.
Results of national survey showed 49% of women aged 13 to 17 years had received at least one dose of HPV vaccine by 2010, and 32% reported having received all three doses. Estimated effectiveness of at least one vaccine dose is 82%, according to the researchers.
To assess the impact of the vaccine on HPV infection rates, Markowitz and colleagues compared data from the National Health and Nutrition Survey Evaluation (NHANES) from the pre-vaccine era (2003-2005) with 2007 to 2010 NHANES data.
HPV infection rates were determine based on linear array HPV assays of cervicovaginal swabs obtained from female participants aged 14 to 59 years. A total of 4,150 participants provided usable swabs from 2003 to 2006, and 4,253 from 2007 to 2010. History of HPV vaccination was determined through interviews with NHANES participants or their parents if they were younger than 16.
Overall, HPV prevalence declined from 42.5% in 2003 to 2006 to 39.8% in 2007 to 2010 — a nonsignificant difference.
But stratification by age group showed a considerable reduction among women and girls 14 to 19 years. Among this age group, infection with:
- Any type of HPV strain declined from 32.9% to 26.1% (HR 0.79; 95% CI: 0.66-0.95; P=0.01)
- HPV strains included in the vaccine declined from 11.5% to 5.1% (HR=0.44; 95% CI: 0.31-0.62, P<0.001)
- Oncogenic HPV strains included in the vaccine declined from 7.2% to 3.6% (HR 0.50, 95%f CI 0.34-0.74, P<0.001)
- Oncogenic hPV strains not included in the vaccine declined from 20.7% to 16.4% (HR 0.79, 95% CI 0.60-1.04)
The investigators found no significant differences between pre-vaccine and post-vaccine HPV rates for age groups 20 to 24, 25 to 29, 30 to 39, 40 to 49, or 50 to 59.
Although HPV vaccine uptake is not widespread enough, it is increasing, the researchers noted. In 2010, 49% of 13- to 17-year-olds received at least one dose, up from 25% in 2007.
“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,” CDC Director Tom Frieden said in a press release. “For every year we delay in doing so, another 4,400 girls will develop cervical cancer in their lifetimes.”