How was the effectiveness of the vaccines proven?

We know that carcinogenesis from genital types of HPV in the lower reproductive system and the anus is a drawn out process, and that premalignant lesions appear before invasive cancer does.
The studies conducted before the first vaccines became available proved their effectiveness in preventing premalignant lesions that lead to cervical cancer (as well as genital warts in the case of Gardasil).

The studies on Gardasil 9 focused from the start on the prevention of premalignant lesions in multiple organs:

  • in women (uterine cervix, vagina, vulva, and anus)
  • and in men (anus and penis)

as well as on the prevention of genital warts in women and men.

The vaccine was proven 100% effective as regards the prevention of the above lesions caused by the 9 types of HPV it protects from.