Genital HPV infections are categorized as including either high risk or low risk strains. These different HPV strains are referred to by numbers (instead of names). The two most frequent high risk strains are 16 and 18, and they are associated with 70% of the cancers of the cervix which occur in the United States. The two most common low risk strains are 6 and 11, and they are associated with 90% of genital warts cases; these strains do not have any potential to progress into a malignancy but can be extremely contagious.
High risk strains (16 and 18) are frequently associated with HPV infections that persist and do not resolve spontaneously over time. The low risk strains (6 and 11) do not have any potential to progress to cancer of the cervix but can spread rapidly to new sites both on the person infected and to their partners.
Gardasil is an FDA approved vaccine which has been demonstrated to be protective against HPV. Gardasil is a quadrivalent virus that protects against four strains of HPV: 16 and 18 (the more aggressive strains that cause cervical cancer) and 6 and 11 (the less aggressive strains which cause highly contagious genital warts). Gardasil will give immunity to all four strains, but the vaccine is preventive, so it will only be effective against these strains if the person has not yet been exposed prior to receiving the virus.
The vaccine is extremely effective in preventing persistent infections and diseases caused by the HPV strains included in the vaccine, but only in those cases where the person has not been previously exposed to those specific viral strains before having received the vaccine. The vaccines are not therapeutic and cannot be used to treat active infection or disease, even if caused by vaccine-covered strains.
The Gardasil vaccine consists of a series of three injections over a six month period of time. The usual schedule is the initial injection, the second injection being given two months later and the third injection being given four months after the second. The shots are given in the arm.