Decline in CIN2+ in younger women after HPV vaccine introduced



The introduction of human papillomavirus vaccination in the United States in 2006 was associated with a significant decrease in the rates of cervical intraepithelial neoplasia grades 2 and above (CIN2+) in younger women.

The overall rate of CIN2+ declined from an estimated 216,000 cases in 2008 – 55% of which were in women aged 18-29 years – to 196,000 cases in 2016, of which 36% were in women aged 18-29 years, according to analysis of data from the Human Papillomavirus Vaccine Impact Monitoring Program (MMWR. 2019 Apr 19;68:337-43.

In 2008, the highest rates of CIN2+ were seen in women aged 20-24 years and decreased with age, but in 2016, the highest rates were in women aged 25-29 years. The rates of CIN2+ declined significantly in women aged 18-19 years from 2008-2016, but increased in women aged 40-64 years.

In 2008 and 2016, around three-quarters of all CIN2+ cases were attributable to HPV types that are targeted by the HPV vaccine. However the rates of vaccine-preventable CIN2+ declined among women aged 18-24 years, from 52% in 2008 to 30% in 2016.

“Both the estimated number and rates of U.S. CIN2+ cases in this report must be interpreted in the context of cervical cancer prevention strategies, including HPV vaccination and cervical cancer screening,” wrote Nancy M. McClung, PhD, of the Epidemic Intelligence Service at the Centers for Disease Control and Prevention and coauthors.

Notably, the screening interval for cervical cancer was increased from yearly in 2008 to once in 3 years with cytology alone or once in 5 years with cytology plus HPV testing for women aged 30 or above in 2016.

“Older age at screening initiation, longer screening intervals, and more conservative management in young women might be expected to reduce the number of CIN2+ cases detected in younger age groups in whom lesions are most likely to regress and shift detection of some CIN2+ to older age groups, resulting in a transient increase in rates,” Dr. McClung and colleagues wrote.

However they noted that the decrease in HPV 16/18–attributable CIN2+ rates among younger age groups was likely a reflection of the impact of the introduction of the quadrivalent vaccine immunization program.

One author declared personal fees from Merck during the course of the study. No other conflicts of interest were declared.

SOURCE: McClung N et al. MMWR. 2019 Apr 19;68:337-43.

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