A new analysis indicates that rates of high-grade cervical lesions decreased in young US women after vaccines were made available to protect against human papillomavirus (HPV), but the trend may be due in part to changes in cervical cancer screening recommendations. The study illustrates some of the challenges in monitoring a vaccine’s impact during a time of concurrent changes in screening.
More than half of high-grade cervical lesions, which are abnormal tissue changes that can lead to cancer, are caused by persistent HPV infection that can be prevented if a person receives an HPV vaccine. Monitoring trends in the incidence of these lesions is helpful for evaluating the impact of HPV vaccination.
A team led by Dr Susan Hariri, of the US Centres for Disease Control and Prevention, found that in the first few years after HPV vaccination was introduced in the US (2008-2012), there were large and uniform declines in high-grade cervical lesions in young women across the country who were aged 18 to 20 years, and to a lesser extent, in women aged 21 to 24 years.
Hariri noted that high-grade cervical lesions are asymptomatic and can only be detected through routine cervical cancer screening. Because screening recommendations were changing during the time period of this study, the investigators also looked at trends in cervical cancer screening utilisation. “In particular, screening is no longer recommended in women before age 21 years, and we found substantial declines in screening in 18 to 20 year olds that were consistent with the new recommendations,” said Hariri. While screening also declined in 21 to 24 year old women, the decreases in screening were much smaller. “We think that the decreases in high-grade lesions in this group reflect changes in screening but also may be partially due to HPV vaccination.”
Hariri added that the greatest benefit of HPV vaccination – reducing the burden of cervical cancer and other HPV-associated cancers – will take many years to evaluate because of the long lag time between infection with HPV and the development of cancer.
Cervical intraepithelial neoplasia grade 2, 3, and adenocarcinoma in situ (CIN2+) lesions can be monitored as early indicators of human papillomavirus (HPV) vaccine impact. Changes to screening utilization will affect observed reductions in CIN2+ rates and complicate the interpretation of vaccine impact.
From 2008 to 2012, 9119 cases of CIN2+ among 18- to 39-year-old residents of catchment areas in California, Connecticut, New York, and Oregon were reported to the HPV-IMPACT Project, a sentinel system for monitoring the population impact of HPV vaccine. Age-stratified CIN2+ incidence rates were calculated for each catchment. Annual cervical screening was estimated for California, New York, and Oregon catchments with administrative and survey data. The Cochran-Armitage test was used to examine trends.
From 2008 to 2012, the incidence of CIN2+ significantly decreased among 18- to 20-year-olds (California, from 94 to 5 per 100,000 women; Connecticut, from 450 to 57 per 100,000 women; New York, from 299 to 43 per 100,000 women; and Oregon, from 202 to 37 per 100,000 women; Ptrend < .0001) and among 21- to 29-year-olds in Connecticut (from 762 to 589 per 100,000 women) and New York (from 770 to 465 per 100,000 women; Ptrend < .001); rates did not differ among 30- to 39-year-olds. During the same period, screening rates also declined, with the largest decreases among 18- to 20-year-olds (from 67% in Oregon to 88% in California) and with smaller declines among 21- to 29-year-olds (13%-27%) and 30- to 39-year-olds (3%-21%).
The declines in CIN2+ detection in young women were likely due to reduced screening but could also reflect the impact of vaccination. These data illustrate challenges in interpreting CIN2+ ecologic trends in the new era of cervical cancer prevention and emphasise the importance of information such as HPV types detected in lesions to assess the impact of HPV vaccine on cervical precancers.