Modelling patterns of clearance of HPV-16 infection and vaccination efficacy

A model representing carcinogenic HPV infection transmission dynamics and cervical cancer natural history was adapted to assess the consequences of introducing vaccination against HPV-16 infection. Alternative scenarios either allowing repeated infections with the HPV-16 (i.e. SIS scenario) or assuming that clearance of infection occurs through the development of a long lasting, specific immune response which protects against re-infection (i.e. SIR scenario) were investigated. The difference in reduction in lifetime cervical cancer achieved through vaccination of 12-year-old girls, between SIS and SIR scenarios, was up to 25% of expected cases in an unscreened population. This difference increased to 30% when vaccination of 12-year-old boys was also included as an intervention. The role of SIS or SIR dynamics should be accounted for in the assessment of model-based projections of the effectiveness of vaccination programmes, until available data about the transmission dynamics support the accuracy of model predictions.