HPV or Human papillomavirus is a viral infection transmitted through skin-to-skin contact.
There are over 100 varieties of HPV, more than 40 are passed through sexual contact and can affect genitals, mouth, or throat.
The Centers for Disease Control and Prevention (CDC), stated that HPV is the most common sexually transmitted infection (STI).
Although some cases of genital HPV infection may not lead to any health problems, some types can cause genital warts or even cancers of the cervix, anus, and throat 
Various strains of HPV are associated with most cases of cervical cancer which is the second cause of death from cancer among women worldwide after breast cancer .
There are 3 types of HPV vaccines:
Bivalent HPV vaccine (Cervarix):
protects against HPV types 16 and 18
quadrivalent HPV vaccine (Gardasil): it protects against 4 types of HPV 6, 11, 16 and 18.
9-valent HPV vaccine (Gardasil 9):
protects against HPV types 6, 11, 16, 18, 31, 33, 45, 52, and 58.
These three vaccines have been licensed by the FDA and all of them protect against HPV types 16 and 18 that cause most HPV cancers.
The Centers for Disease Control and Prevention (CDC) recommends receiving the vaccine at around age 11 or 12 years old to ensure that they’re protected against HPV before they have exposure to the virus and it is available to have the vaccines till 45 years old incase they haven't been vaccinated before .
Mechanism of action:
It depends on L1, the major papillomavirus virion protein, which has the ability to assemble into virus like structure (VLS). These VLP are morphologically indistinguishable from the outer shell of authentic virions .
Expression of the L1 protein in yeast using recombinant DNA technology produces noninfectious virus-like particles (VLP) that resemble HPV virions .
The formation of VLP is important for L1 vaccines because:
they can induce high levels of neutralizing antibodies
the L1 epitopes recognized by neutralizing antibodies are conformation dependent, therefore, denatured L1 does not induce neutralizing antibodies and does not protect against HPV.