Population-level impact and herd effects following HPV vaccination programs: a global view

Abstract

Prophylactic HPV-vaccination programs constitute major public-health initiatives worldwide. HPV vaccines have been introduced into national immunization programs in over 80 countries, although most are in high income countries. Now that these vaccines have been implemented just over 10 years, the impact and effectiveness on HPV infection and disease has been reported in various observational studies. Underpinning outcomes, is high coverage of target populations before HPV exposure, as well as those where catchup programs have been initiated. Recently reported are maximal reductions of ∼90% for HPV related infections such as 6/11/16/18, ∼90% for genital warts, ∼45% for low-grade cytological cervical abnormalities, ∼60% for high-grade histologically-proven cervical abnormalities (HSIL), in addition to reductions in colposcopic referrals, plus ablative therapy. With these reductions in HSIL, the positive predictive value of cervical cytology for underlying precancer has reduced: thus countries are adopting more sensitive HPVDNA screening methods. Where catchup programs have extended to high coverage and to up to 26 years of age, herd protection for vaccine-related infections and disease has been seen in unvaccinated women, as well as in similar age males, all from the female only vaccine programs. Modelling suggests that the incremental benefit of vaccinating boys where female coverage is high will be small. However, that does not address gender neutral (male) vaccination.