Reduced dose human papillomavirus vaccination: An update of the current state-of-the-art

Human papillomavirus (HPV) infection is the primary cause of genital warts, some oropharyngeal cancers and anogenital cancers, including cervical, vagina, vulvar, anal and penile cancers. Primary prevention of cervical cancer requires the prevention of high-risk HPV infections, particularly HPV genotypes 16 and 18. Both Gardasil®  and Cervarix®  vaccines when administered by a three-dose schedule have been demonstrated to be effective against cervical, vulva, and vaginal cancer precursors from vaccine genotypes in phase III clinical trials, and post-marketing studies; Gardasil®  vaccine also offers additional protection against anal cancer precursors. However, high costs of HPV vaccines and the logistics of delivering a three-dose schedule over 6 months are challenging in countries with limited resources. Several studies have demonstrated non-inferiority in antibody response between adolescents (9-15 years old) who received two doses (6 months apart) and women (>15 years old) who received the standard three-dose schedule. These studies provided evidence for the World Health Organization and European Medical Association to revise its recommendation to give two instead of three doses of HPV vaccine to adolescents below 15 years of age, provided the 2nd dose is given 6 months apart. Although reduced dose schedules can alleviate costs and logistics associated with HPV vaccination, especially in resource-poor countries, there are still gaps in this area of research, particularly regarding long-term protection. This review discusses the findings on antibody response and clinical outcomes in studies evaluating reduced dose HPV schedules, and highlights the important considerations of its implementation. In addition, other important immunological biomarkers that may be associated with long-term protection are highlighted and discussed.