Vaginal immunization efficacy is not supported by many studies. A dilemma facing prophylactic vaccine design is that IgA cervical secretions would be effective in neutralizing infecting viral particles but would not control already existing infections. Tindle et al. The immune response mechanisms associated with disease progression are not clearly understood. Selective cross reactivity of HPV types limits the use of a non-type specific vaccine.
Some untreated individuals have spontaneous disease regression.
High lifetime risk of exposure. Thus, several questions are raised. Who should be immunized and when as well as the universal efficacy and cost of a prophylaxis vaccine are potential problems. Specifically, such vaccines would target E1 and E2, proteins involved with viral replication by stimulating a CTL response. E1 and E2 are the preferred targets compared to other E proteins since they are produced early in the viral cycle in the replicating basal stem cells that are the primary reservoirs for new virus.