Routine school-based HPV immunisation was offered to girls aged 12-13 in Scotland from 2008, with a catch-up programme over 3 years for 14-18 year old girls. To date, we have shown that vaccination of catch-up cohorts is associated with a significant decrease in prevalence of HPV 16/18/31/33/45, in cervical intraepithelial neoplasia of all grades and in cytology performance, particularly the predictive value of low-grade cytology. This reduction is achieved despite probable exposure to HPV before immunisation, particularly of the older catch-up girls.
The first cohort immunised at age 12-13 entered the Scottish Cervical Screening Programme in September 2015 at age 20. A further decline in HPV 16/18/31/33/45 prevalence was observed in these women when compared to the catch-up population. Evidence of herd immunity in the unvaccinated population has also emerged, including for cross-protective types.
To complement the work on viral outcomes we will present data on (1) the level of CIN (2) the performance of cytology in the routinely immunised cohort.
The Scottish Cervical Call Recall System - the national IT system containing all screening records and also vaccination status - will be interrogated. By June 2017 we will have a minimum of 12 months follow-up on all 31,000 routinely immunised women invited for screening. Linked data on degree of immunisation, on cytological abnormalities and on histological diagnosis following referral for colposcopy will be used to calculate odds ratios by immunisation status for cytological abnormality and histological diagnosis. The cytological abnormalities will be correlated with histological diagnosis to determine performance of cytology as a screening test
Approximately 31,000 women aged 20 were invited between September 2015 and June 2016. Over 23,000 of these had received 3 doses of vaccine. Initial evidence suggests that high grade disease (CIN2+/HSIL+) is virtually absent routinely immunised females. Before immunisation, CIN 2+ was confirmed in 2.84% of women screened at age 20. In the 1995 cohort (immunised at age 12-13), CIN 2+ is present in 0.33% of women. Comprehensive data on disease prevalence and on the performance of cytology as a screening test will be presented.
This will be the first population-based demonstration of the clinical effect of bivalent HPV immunisation of girls who are likely to have been HPV-naive at the time of vaccination. The information presented will be of great importance for the design and delivery of screening programmes in all highly vaccinated populations, and for planning cancer prevention strategies in resource-poor countries.