DEAR MAYO CLINIC: Why is the HPV vaccine now offered to adults and adolescents? I was surprised to hear that it’s recommended up to age 45. Will the vaccine do any good for adults who already have HPV?

ANSWER: The Centers for Disease Control and Prevention (CDC) now recommends that some adults ages 27 to 45 talk with their health care provider about the human papillomavirus, or HPV, vaccine. The vaccine isn’t necessary for everyone in that age group. The focus is on people who weren’t vaccinated when they were younger and are at risk for infection. If you’re older than 26 and aren’t sure if you need the vaccine, ask your health care provider.

Although the HPV vaccine can prevent a new HPV infection, it cannot treat one you already have.

HPV is the most common sexually transmitted infection in the U.S. Almost all sexually active people get an HPV infection at some point. In many cases, HPV may not cause symptoms or lead to health concerns, and the body clears the infection without any problems. But certain strains of HPV are dangerous viruses that can lead to cancer and genital warts.

Two strains of HPV cause 70 percent of all cervical cancer and cervical precancerous lesions. Once cervical cancer develops, it is difficult to treat and can be life-threatening. HPV infections also can lead to other genital and anal cancers in females, as well as penile cancer and anal cancer in males. In addition, HPV causes most oral and throat cancers, as well as genital warts in men and women.

The HPV vaccine has proven to be a safe and effective way to prevent HPV infection. But it can’t cure an existing infection. So the best time to get the vaccine is before you are exposed to the virus. That means it’s ideal to be fully vaccinated before becoming sexually active. The vaccine is most effective and has been most extensively studied in children between the ages of 9 and 14.