HPV HANDBOOK - Zervita

THE POTENTIAL PUBLIC HEALTH IMPACT OF VACCINES AGAINST HPVVaccine efficacy and effectiveness• Efficacy: measures how well an intervention can work underideal conditions, such as a vaccine trial• Effectiveness: measures the impact of an intervention undermore realistic conditions: for example, in an immunizationprogramme that does not vaccinate 100% of the targetpopulationHPV clinical vaccine trials should provide data on the ‘efficacy’ of thevaccine, but how this factor relates to take, degree and also durationof protection may be unclear. However, the very high seroconversionrate in early clinical trials, together with the high level of protection inanimal models, suggests that there could be a high take against theparticular viral types included in the vaccine.Model definitionTo advance from simple theory, we developed a compartmental,deterministic model and applied it to the question of whether womenand men, or women only, should be vaccinated (see box on page 66).For both squamous intraepithelial lesions (SIL) and CC, at highvaccination coverage, the additional benefit achieved by vaccinatingmen as well as women is small. For men, the HPV vaccine would carrythe risks of immunization but little benefit, although the inclusion oflow-risk HPV types 6 and 11 would potentially decrease the incidenceof genital warts. 11 There may also be immunological reasons whyimmunization should be confined to women: if breakthrough infectionsdo occur among vaccinated women, mucosal antibodies coating theshed virus may neutralize the virus and stop transmission tosusceptible men, thus reducing the need for men to be vaccinated (JSchiller, personal communication). If vaccination of men carries littlebenefit, then resources could be conserved and public strategiesshould concentrate on vaccinating women only.65