What it prevents: HPV is a group of 40 human papillomaviruses that can be transmitted through sexual contact — it’s estimated by the CDC that at least 50 percent of sexually active men and women have been infected by the time they’re 50. While most infections will go away without treatment, the vaccine protects against the four types of HPV that are most commonly linked to more serious conditions. Types 16 and 18 can cause cervical cancer as well as other types of cancer. Types 6 and 11 cause up to 90 percent of genital warts. Since the vaccine only works if it’s given before a person is infected with HPV, it’s recommended for girls at 11 to 12, before they become sexually active. In 2011, the CDC began recommending that all 11- to 12-year-old boys receive the vaccine as well.

When it’s given: The HPV vaccine is given in three doses in kids aged 11 to 12 years old, though it can be given as young as nine years old. The second shot is given two months after the first; the third is given six months after the first.

What you may have heard: There have been several claims that the HPV vaccine can cause different severe reactions. The CDC has not determined that any of these reported conditions can truly be linked to the vaccine. Keep in mind that the vaccine has been tested in more than 11,000 women and found to be safe.

Risk of a reaction: Mild side effects include redness, soreness, itching or swelling at the injection site. One in 10 may experience a mild fever. More rarely (1 in 65), a child may experience a moderate fever.