The proportion of cervical precancers positive for HPV types 16 and 18 declined significantly between 2008 and 2014, particularly among vaccinated women, according to a study published in Cancer Epidemiology, Biomarkers & Prevention.
The findings confirm the impact of vaccination with the quadrivalent HPV vaccine, administered predominantly between 2006 and 2015 in the United States, and HPV 9-valent vaccine (Gardasil 9, Merck), which currently is the only vaccine used in the U.S.
“Almost all sexually active individuals will get HPV at some point in their lifetime, but most HPV infections go away on their own without any treatment,” Nancy M. McClung, PhD, RN, epidemic intelligence service officer at CDC, said in a press release. “If an HPV infection does not go away, it can cause cell changes that, over time, develop into a lesion on the cervix called a cervical precancer. Cervical precancers allow us to observe the impact of HPV vaccination earlier than cervical cancer, which can take decades to develop.”
McClung and colleagues assessed data from the population-based HPV Vaccine Impact Monitoring Project (HPV-IMPACT), established by the CDC in 2008 to track trends in cervical precancer incidence. They tested archived specimens taken between 2008 and 2014 from women aged 18 to 39 years with cervical intraepithelial neoplasia grade 2 to grade 3 or adenocarcinoma in situ (CIN2+) for 37 types of HPV. Researchers evaluated the percentage and estimated number of CIN2+ cases by HPV types over time. They used Cochrane-Armitage tests to identify trends in HPV16/18-positive CIN2+, including overall and by vaccination status, age, histologic grade and race/ethnicity.
Of 10,206 specimens (mean age, 28 years; 53% non-Hispanic white) for which HPV typing results were valid, 9,948 (97.5%) were positive for HPV.
Most specimens (77.8%) had only one HPV type. Of the specimens with multiple HPV types, most (77.7%) had two types (range, 2-14) and 53.9% included HPV16/18.
HPV-IMPACT documented a 21% reduction in CIN2+ cases between 2008 and 2014, from 2,444 to 1,857 cases. The proportion of HPV16/18-positive cases decreased from 52.7% (n = 1,235) in 2008 to 44.1% (n = 819) in 2014 (P < .001).
The proportion of cases linked to HPV types 31, 33, 45, 52 and 58 increased from 23.9% in 2008 to 31% in 2014 (P < .001); however, the estimated number of these cases remained steady when applying the proportion to the declining overall incidence.
During the study period, the percentage of HPV16/18-positive CIN2+ cases decreased among vaccinated women (55.2% vs. 33.3%; P < .001), unvaccinated women (51% vs. 47.3%; P = .003) and women with unknown vaccination status (53.7% vs. 45.8%; P < .001).
The researchers hypothesized that the decrease among unvaccinated women may be attributable to “herd protection,” which can be conferred through vaccination or immunity acquired from previous infection.
Researchers also observed significant decreases in the percentage of HPV16/18-positive CIN2+ cases among women aged 18 to 20 years (48.7% vs. 18.8%; P = .02), 21 to 24 years (53.8% vs. 44%; P < .001), 25 to 29 years (56.9% vs. 42.4%; P < .001), and 30 to 34 years (49.8% vs. 45.8%; P = .04), but not among women aged 35 to 39 years (46.1% vs. 45%).
Results also showed significant declines in the proportion of HPV16/18-positive CIN2+ among non-Hispanic white women (59.5% vs. 47.9%) and non-Hispanic black women (40.7% vs. 26.5%; P < .001 for both), but not among Hispanic women (44% vs. 40.1%) or Asian women (42.6% vs. 49.3%).
The researchers acknowledged study limitations, including the inability to confirm vaccination status in approximately half of the women evaluated.
Recent CDC data show that 49.5% of girls and 37.5% of boys aged 13 to 17 years are current on all recommended doses of the HPV vaccine.
McClung advised clinicians to strongly recommend the vaccine to all preteens at ages 11 or 12 years and address parents’ questions and concerns.
“This is clear evidence that the HPV vaccine is working to prevent cervical disease in young women in the United States,” McClung said in the release. “In the coming years, we should see even greater impact as more women are vaccinated during early adolescence and before exposure to HPV.” – by Jennifer Byrne
Disclosures: The authors report no relevant disclosures.