Early Direct and Indirect Impact of Quadrivalent HPV (4HPV) Vaccine on Genital Warts: a Systematic Review

Introduction: Since 2007, many countries have implemented national human papillomavirus (HPV) vaccination programs with the quadrivalent HPV (4HPV) vaccine that has been shown to be efficacious in clinical trials involving 25,000 subjects. Two vaccine serotypes, HPV16 and 18, are responsible for cervical cancer and other HPV-related cancers, but the impact of the 4HPV vaccine on these cancers cannot be seen immediately as there is a considerable lag between infection with HPV and cancer development. The other two serotypes, HPV6 and 11, are responsible for genital warts (GWs), which develop within a few months after infection, making GWs an early clinical endpoint for the assessment of the impact of 4HPV vaccination. Methods: We performed a systematic literature search in PubMed to identify all published studies on 4HPV vaccination, including those that assessed the impact of 4HPV vaccination programs on the incidence of GWs at a population level around the world. Results: A total of 354 records were identified in the PubMed search. After screening and obtaining full papers for 56 publications, 16 publications presenting data on the impact or effectiveness of 4HPV vaccination on GWs were identified. These reported data on the impact or effectiveness of 4HPV in six countries [Australia (n = 6), New Zealand (n = 2), United States (n = 3), Denmark (n = 2), Germany (n = 1), and Sweden (n = 2)]. In Australia, no GWs were diagnosed in women aged <21 years who reported being vaccinated. A 92.6% reduction in GWs incidence was reported for all women in this age group, where the vaccine uptake rate (VUR) was 70% for 3 doses. The highest reductions were reported in countries with high VURs, mostly through school-based vaccination programs, although high VURs were obtained with some non-school-based programs. Conclusion: The results are coherent with the GWs incidence reduction reported in clinical trials and are an early indicator of what can be expected for the long-term clinical impact on vaccine-type HPV-related cancers.