Cervical Precancers in the U.S., 2008 vs 2016: Falling Among Young Women After HPV Vaccine

Human papillomavirus (HPV) causes about 30,000 cancers a year in the United States, and cervical cancer is the most common of them in women. HPV vaccination began in 2006. Cancers take decades to develop, but high-grade cervical lesions — cervical intraepithelial neoplasia grades 2 and 3 and adenocarcinoma in situ, together called CIN2+ — appear within a few years of infection and are found through screening, so they're used to track the vaccine's impact.

CDC used HPV-IMPACT, a population-based surveillance system covering about 1.5 million women in five areas — New Haven County, Connecticut; Monroe County, New York; Davidson County, Tennessee; and parts of Alameda County, California, and Washington and Multnomah counties, Oregon — to estimate national CIN2+ cases for the first time from population data.

Key findings

• Rates fell sharply among women 18–19 and 20–24 and rose among women 40–64.
• In 2016, 150,000 cases were caused by the 9-valent vaccine's HPV types: 84,000 by types 16/18 and 66,000 by types 31/33/45/52/58.

Rates by age

Estimated number of diagnosed CIN2+ cases by age group, United States, 2008 and 2016. From CDC's MMWR.

In 2016, cases split 71,000 (36%) among women 18–29, 74,000 (38%) among women 30–39 and 51,000 (26%) among women 40 and older. Among women 18–24, only 30% of cases were caused by HPV 16/18.

Estimated CIN2+ cases by HPV type group, United States, 2016. From CDC's MMWR.

Vaccination and screening both shape the numbers

• Vaccination: HPV vaccine has been recommended since 2006 at ages 11–12, with catch-up through 26. The quadrivalent vaccine (HPV 6, 11, 16, 18) was used until 2015 and the 9-valent vaccine (adding 31, 33, 45, 52, 58) since 2016. In 2016, 65.1% of girls aged 13–17 had at least one dose and 43.0% three doses. The drop in HPV 16/18 lesions among young women reflects the vaccination program.
• Screening: in 2008, screening started within 3 years of first sex or by age 21, often yearly. By 2016 it started at 21, every 3 years with a Pap test, or every 5 years with Pap plus HPV testing from age 30. Later, less frequent screening and more conservative care in young women — whose lesions often regress — shift detection to older ages, and more sensitive HPV testing may add to the rise among older women.

The earlier national estimate, 177,469 cases in 2000, came from claims data for privately insured women.

Limits: the five surveillance areas aren't nationally representative (they have somewhat more Black and Asian women and fewer Hispanic women), and estimates weren't adjusted for race or screening habits — plausible ranges were 159,000–283,000 for the prevaccine era and 179,000–210,000 for 2016. HPV types for women 40 and older were assumed from women 30–39, which may overstate vaccine types. And the effects of screening changes and vaccination can't be fully separated, though earlier studies show screening changes don't fully explain the declines.

Increasing HPV vaccination at ages 11–12, with catch-up through 26, will further reduce cervical precancers.

Sources

Based on McClung NM, Gargano JW, Park IU, et al., "Estimated Number of Cases of High-Grade Cervical Lesions Diagnosed Among Women — United States, 2008 and 2016," Morbidity and Mortality Weekly Report 68(15), CDC; a work of the United States government in the public domain.