The vaccine is only for girls who have not yet had sex as the vaccine will only prevent an infection and will do nothing for someone who is already infected. It will only protect against the 2 strains that most often cause genital warts and the 2 strains that most often cause cervical cancer. It will not protect against the dozens of other strains that exist.

BTW, the only "safe" sex to prevent the transfer of HPV is no sex.