The reduction of HPV infection and associated lesions as a consequence of national HPV vaccination programmes is now being realised in various countries. As current and proposed cervical screening modalities are largely calibrated to disease levels pre vaccination, their performance will undoubtedly be affected as a consequence of the shifting pattern of infection and disease. The aim of this paper is to outline the challenges in defining optimal screening methods for immunised women.
Scotland is a country with an organised call-recall cervical screening programme, which has also benefitted from a successful national HPV female vaccination programme since 2008 associated with uptake of over 90% in 12-13 year old girls since its introduction. As Scotland initiates cervical screening aged 20, and incorporated an initial 3 year vaccine “catch up” campaign for girls up to the age of 18, immunised women have been entering the cervical screening programme since 2010. Outputs of the National HPV epidemiology and surveillance programme and associated research will be presented which will provide insight into the performance of cytology and HPV based primary screening in immunised women.
At the population level, a significant reduction in HPV infection and disease is associated with vaccination in Scotland. Screening uptake is higher in women immunised as part of catch up compared to unimmunised women. The prevalence of HPV 16, 18, 31, 33, 45 has decreased significantly, as a consequence of a three dose vaccine schedule although a one dose effect on 16/18 infection was also observed. The predictive value of cytology in immunised women reduces significantly, particularly that of low-grade cytology for CIN2+. While a reduction of HPV 16/18 using clinically validated HPV tests has been observed a proportionate increase of HPV “other” may reduce the specificity of “HPV first” strategies. Triage of HPV first infection using 16/18 typing in immunised women will have diminishing returns as less that 10% of residual HPV infections will be positive for one of those types.
While vaccinated women appear to be willing to engage in screening the predictive performance of cytology will reduce. While this justifies the introduction of more objective tests, HPV first strategies in immunised women will require robust triage given that residual infections will largely be composed of those known to confer a low risk of significant disease.