I know that I don't have this correct, because I received the explanation a good while ago, but the Gardasil fights the HPV virus in females because the female tract is lined with..you guessed it....squamous cells! Squamous cells are the cells that line most moist tracts in the body. The male doesn't have the same system. If he carries the virus, it is in a different place and in a different form that is not susceptible to the Gardisil. The anatomy of males and females are different....duh!....so while we think that we should be giving the boys the Gardisil like the girls, that is not the case. They might be able to use the same science and develop a vaccine for males, but it will have to be different.

I think that the Gardisil prevents the virus from establishing itself in the squamous tissue, rather than killing it after it is there. That is why you give it to girls who (you hope!) are not sexually active yet, before they can have been exposed to the virus.

I wish I remembered better what I was told. sorry..this is pretty sketchy.