The majority of American adults are unaware that the most common sexually transmitted disease, HPV, or human papillomavirus, can lead to a variety of cancers, according to research released Monday.

"More than 70 percent don't know that HPV causes anal, penile and oral cancers," said Ashish Deshmukh, author of the new study and assistant professor at UTHealth School of Public Health in Houston.

He called the vast gap in public awareness shocking, and suggested it's one reason why national HPV vaccination rates are so low.

For the study, Deshmukh and his colleagues analyzed National Cancer Institute data of 6,261 men and women who were surveyed about their HPV knowledge in 2017 and 2018. Respondents were between the ages of 18 and 101.

Two-thirds of women 18 to 26 understood that HPV can cause cervical cancer, compared with just one-third of men of the same age.

But HPV has also been shown to cause oral, anal and penile cancers, a fact lost on 80 percent of men and 75 percent of the women in that same age range in the study, which was published in in the journal JAMA Pediatrics.

Overall, 70 percent of adults of any age were unaware of the link between HPV and other cancers.

The first HPV vaccine was recommended in 2006 for girls only as a way to prevent cervical cancer. But since then, the science has shown men, too, are at risk for HPV-related cancers, as well as conditions like genital warts. Boys weren't added to the HPV vaccine recommendation schedule until 2011.

"Because of that time lag, there is this historic perception that HPV is a disease among women, that it only causes cervical cancer," Deshmukh told NBC News.

Currently, the CDC recommends that everyone up through age 26 get the HPV vaccine, starting around age 9, long before they may be exposed to the virus, which is transmitted through sexual contact.

Kids need two shots, six months apart; teens and young adults over age 15 need three doses. Unvaccinated people up through age 45 may also get the shots based on personal HPV risks.

Nationally, HPV vaccination rates hover just below 50 percent, with a notable lag in boys' coverage rates.

Just about 44 percent of boys get the vaccine, compared with 53 percent of girls, according to the CDC.

The researchers theorize that if the knowledge gap were to be narrowed, more parents would get their children vaccinated.

The new study showed that more than half of adults between 27 and 45 were unaware of the link between HPV and penile, oral and anal cancers.

"Low levels of HPV knowledge in these older age groups is particularly concerning, given that these individuals are (or will likely be) parents responsible for making HPV vaccination decisions for their children," Kalyani Sonawane, assistant professor at the University of Texas School of Public Health, wrote in a news release.

A study published last week showed another possible benefit to HPV vaccination: herd immunity. Researchers found that when girls and young women are vaccinated, young men who haven't received the shots may be protected against HPV-related cancers.

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