You’d think a shot that protects against the most common sexually transmitted disease would be in high demand, but many people who should be getting it are skipping the human papillomavirus (HPV) vaccine.

The Centers for Disease Control and Prevention (CDC) recommends the HPV shot for boys and girls beginning at age 11 or 12. But the latest CDC data shows that just 42 percent of girls and 28 percent of boys age 13 to 17 are fully vaccinated against the disease.

In fact, vaccination rates have fallen so low that pharmaceutical company GlaxoSmithKline recently announced that it would no longer manufacture its HPV vaccine, Cervarix. Another pharmaceutical company, Merck, will continue to make its HPV vaccine, Gardasil.

Those low vaccination rates can come at a high cost.

“HPV can cause genital warts and several types of cancer, many of which can be prevented by the vaccine,” says Consumer Reports medical director Orly Avitzur, M.D. “For example, about 13,000 women are diagnosed with cervical cancer annually, and the majority of those cases are caused by HPV.”

An estimated 14 million people in the U.S. contract HPV every year, according to the CDC. Debbie Faslow, Ph.D., the senior director for HPV and women's cancers at the American Cancer Society, adds that “each year HPV causes about 30,700 cancers in men and women, and HPV vaccination can prevent about 28,500—or 90 percent— of these cancers."

STDs On the Rise

According to a new report from the CDC, sexually transmitted disease (STD) rates in general are at an unprecedented high in the U.S. and rising fast. For example, in 2015 there were more than 1.5 million cases of chlamydia, up 5.9 percent from 2014; 395,216 cases of gonorrhea, up 12.8 percent from 2014; and 23,872 cases of syphilis, a 19 percent jump from 2014.

While HPV wasn’t part of this report, "if other STDs are increasing, it’s a concern that people are also being exposed to HPV,” Avitzur says.

HPV Affects Everyone

In addition to being responsible for cervical cancer, HPV also causes vaginal cancers and vulvar cancers. But HPV-related cancer is a concern for men, too. It is the culprit in about 95 percent of cases of anal cancer and 35 percent of cases of penile cancer, as well as two-thirds of the more than 48,000 annually diagnosed cases of throat and mouth cancer. While these oral cancers affect both men and women, they are twice as likely to occur in men, according to the American Cancer Society.

HPV-related mouth and throat cancers have been rising so dramatically over the past few decades that some researchers predict that the number of cases will surpass those of cervical cancer by the year 2020.

Why the surge? Researchers aren’t entirely sure, but since HPV is transmitted through genital contact, some think that it could be a result of an increase in people engaging in oral sex.

The Best Protection Against HPV

“There’s no doubt in my mind that getting vaccinated is the best way to protect against HPV,” Avitzur says. And the most effective time to do it? At age 11 or 12.   

This is the age when the shot provides the most protection. “People in this age group are less likely to have had sex, and thus already acquired the disease,” Avitzur says. In addition, according to the CDC the vaccine produces a more robust immune response during the preteen years.

And becoming fully protected just got easier. Originally, the HPV vaccine involved getting three shots, but the Advisory Committee on Immunization Practices (ACIP) revised its guidelines in October. People between ages 9 and 14 now need just two shots instead of three. According to ACIP, when given at this age, two shots—with the second dose administered 6 to 12 months after the first—provide as much protection as the standard three-dose vaccine.

However, women age 15 to 26 and men age 15 to 21 who haven’t previously been vaccinated still need three shots. They should get the second shot one or two months after the first, then a third shot six months after the first one. Men who have sex with men and people who have compromised immune systems (including HIV) can get vaccinated through age 26, if they did not get the HPV vaccine when they were younger, according to the CDC.

If you already have the type of HPV that causes genital warts it’s still a good idea to get the shots if you are within the recommended age groups.

“The vaccine will not cure the disease, but there are many different types of HPV and the vaccine may protect against strains that you may not yet been exposed to,” Avitzur says, “and that could include types that cause cancer.”