BROOKLYN - The New York City Health Department is launching a new subway ad campaign to raise awareness about HPV prevention.

The campaign encourages parents to vaccinate their preteens against the HPV virus, the most common sexually transmitted disease. While the virus is mostly harmless, cervical cancer is overwhelmingly caused by HPV. Getting the vaccination lowers the risk by about 80 percent.

Doctors say preteens are targeted for vaccination because it is best to treat people before they are exposed. While the virus causes cervical cancer in women, doctors also say boys need vaccinations to prevent other HPV-related cancers and transmission of the virus.

The HPV vaccination is a series of three shots over six months.