Methods: An Agent Based Model (ABM) was created, based on input parameters from national databases and scientific literature where available, and best estimates, where data were not available. The model simulates sexual networks and the spread of HPV within these. Simulations represented a “population” of 25.000 individuals. Levels of known parameters (like frequencies of dysplasias and carcinomas in different stages) were used to calibrate the model by letting it run until quasi-steady state was reached without vaccination (baseline). Scenarios were then constructed for vaccination programs covering girls and/or boys and with/without catch-up programs with varying degree of vaccination coverage.

Results: Simulations indicate a substantial impact of vaccination on HPV prevalence. A vaccination efficiency of 70% for only boys or girls will result in significant herd immunity, in effect eradicating HPV in the simulated environment after approximately forty years. The introduction of catch-up programs in the simulation speeds up the eradication rate of HPV. Due to the large herd immunity effect, there are declining marginal yields when vaccinating both sexes and/or increasing the vaccination coverage.

Conclusion: This is a new way of simulating consequences of implementing new health technologies, especially long term results, which are often not available at the time of the assessment. The simulation aims at being more realistic, since it takes individual diversities into account and herd immunity arises as an emergent property of the simulation, but results are dependable on access to the necessary input parameters and assumptions regarding these. The simulations show decreasing impact of increasing vaccination coverage and vaccinating both boys and girls. Based on rational economical analysis, inclusion of both sexes in the vaccination program decreases the cost-effectiveness of the program. There may, however, be ethical concerns regarding equity pointing to different conclusions regarding vaccination coverage.