The HPV vaccine, also called Gardasil, protects against four different strains of the virus that are known to cause most cervical cancers. Before the vaccine, about one in 10 older teenage girls carried one of these high-risk strains; now only 4 percent do. Those four strains also became less common among women in their early 20s, a group with much lower vaccination rates. Now, only 12 percent of these women have the four dangerous HPV strains — a drop from about 19 percent before the vaccine was introduced. Vaccinated women benefitted the most; HPV was less prevalent in that group than in those who hadn’t gotten the shot.

These statistics aren't the only ones in Gardasil's favor. In 2013, federal health officials credited the vaccine with cutting the prevalence of HPV in teenagers by half. And numerous clinical studies have proven the vaccine to be incredibly effective.

But many young women still aren't getting Gardasil — a drug that is administered in three different shots. In 2014, about 60 percent of teenage girls received at least one dose of the vaccine, while only 40 percent received the recommend three doses. And teenage boys, who are often carriers of HPV, didn't fare much better; just 20 percent received all three doses of the vaccine.

These low immunization rates have often been attributed to "knowledge gaps" among parents — notably the myth that the vaccine promotes risky sexual behavior in teenage girls. Some also worry that the HPV vaccine is unsafe, though the drug is rarely associated with adverse health effects. Additionally, the CDC noted that not enough doctors have recommend the vaccine to their patients.