system
Given the following post, respond as if you're commenting on Reddit:
human
Why can't the Gardasil vaccine rid you of the HPV strains you have, but can give protection from the ones that you don't have?
gpt
Gardasil contains the major capsid protein (L1) from different HPV types. Thus, vaccination results in immunity against the viral capsid (the shell of the virus), preventing new infection with HPV. 

However, previous HPV infection that results in viral integration (like what would cause cervical cancer, etc) drives expression of the major HPV oncoproteins, E6 and E7. Gardasil doesn’t contain those proteins, so the vaccine doesn’t induce immunity to them. However, there are several academic and industry groups developing E6 and E7 vaccines that could be used therapeutically to treat previous HPV infection/HPV-associated cancers.