Dra. Leila Catherine Onbargi,

HPV is the most common sexually transmitted infection in the United States and around the world. More than half of sexually active people will be infected with HPV at some time in their lives. Twenty million Americans are currently infected with HPV and another 6 million become infected every year. Half of those newly infected with HPV are between 15 and 24 years of age.

Yes. Most of the time, HPV goes away on its own and doesn't cause any health problems. But sometimes HPV can linger and lead to cervical cancer. Every year in the U.S. approximately 10,000 women develop cervical cancer and 4,000 die from the disease. Cervical cancer is one of the most common cancers in women, killing about 300,000 every year worldwide.

HPV in the genital area is passed from one person to another through genital contact, most often during sex. The best way to avoid HPV infection is to abstain from any sexual activity. You can also lower your chance of getting HPV by having sex with only one person who isn't infected with HPV. But most people who have HPV don't know they have it, so it can be hard to avoid. Although condoms are recommended as a way of decreasing sexually transmitted infections, they don't offer complete protection against HPV.

Not always. Once, cervical cancer was the most common cause of U.S. cancer deaths. The Pap test changed that. HPV infection causes changes in the cervix that can result in cancer. The Pap test is performed by scraping cells from the cervix and examining them to see whether they show changes consistent with the early development of cancer (called precancerous changes). If these changes are detected, the doctor can perform surgery on the affected areas before cancer develops. Typically, the length of time from infection with HPV to development of cervical cancer is decades. So, although most HPV infections occur in teeenagers and young adults, cervical cancer is more common in women during their 40s and 50s.

The Pap test is one of the most effective cancer screening tests, and has dramatically reduced the incidence of cervical cancer in the U.S. But the test isn't entirely predictive of cancer, and not all women get tested as often as they should.

Yes. In June 2006, a vaccine to prevent HPV was licensed by the Food and Drug Administration (FDA) and recommended by a federal advisory commitee to the Centers for Disease Control and Prevention (CDC). Studies in about 21,000 girls and young women found the vaccine was effective in preventing persistent infections caused by four severe types of HPV.

The vaccine is given as a series of three shots. The second shot is given two months after the first, and the third shot is given six months after the first.

The HPV vaccine is recommended for all girls between 11 and 12 years of age. The vaccine can be given to girls as young as 9 years of age. It is also recommended for all teenage and adult women between 13 and 26 years of age if they did not get the vaccine when they were younger.

The HPV vaccine is made using a protein from the surface of the virus. The vaccine protects against four types of HPV: types 6, 11, 16, and 18. Types 16 and 18 are responsible for about 70 percent of cervical cancers. Types 6 and 11 are responsible for about 90 percent of cases of anal and genital warts.

Yes. Because the HPV vaccine is made using only a single protein from each type of the virus, it can't cause HPV, and therefore, can't cause cervical cancer. The most common side effect of the vaccine is redness and tenderness at the injection site. The vaccine may also cause a slight fever.

Yes. Because the HPV vaccine will protect only against HPV types that cause 70 percent of cervical cancers, women should continue to be screened with routine Pap tests.

Yes. The HPV vaccine does not prevent other sexually transmitted infections such as syphilis, gonorrhea chlamydia or herpes. Also, the vaccine doesn't protect against all HPV types.

Probably. Even though boys don't get cervical cancer, the disease is transmitted through sexual contact. So it is likely that the CDC will eventually recommend it for boys, too. Since the initial studies of the HPV vaccine were performed in teenage girls and young women, there isn't much evidence that the vaccine works in boys. However studies in boys are underway.