This week, the federal government reported that nearly half of Americans between the ages of 18 and 59 are infected with genital human papillomavirus — some strains of which can cause deadly cancer. The report, by the National Center for Health Statistics, notes that HPV is the most common sexually transmitted infection in the United States. It also said that some high-risk strains infected 25 percent of men and 20 percent of women, and cause about 31,000 cases of cancer each year.
The good news is that the HPV vaccine is very effective, especially if given in early adolescence. Here are some basics about HPV and the vaccine.
How is the human papillomavirus transmitted?
About 40 strains of HPV are transmitted through direct contact with infected skin or mucous membranes during vaginal, anal and oral sex. Many sexually active people are exposed to the virus by their early 20s, indicating that it is hardly only a risk for people who engage in promiscuous sex.
How serious is the risk of cancer?
Most HPV infections are destroyed by the immune system and cleared from the body within two years, but some strains can persist, including the HPV-16 and HPV-18 strains, which cause most cervical cancers. More than 4,000 women are estimated to die from cervical cancer each year, according to the American Cancer Society. Other strains cause genital warts or cancer of the vagina, vulva, penis, anus, throat and mouth.
How effective is the vaccine?
Recent data from a survey by the Centers for Disease Control and Prevention found that in the decade since the vaccine was introduced, cases of HPV infection in teenage girls had decreased by almost two-thirds. And in women in their early 20s, who have lower vaccination rates and may already have been exposed to the virus before being vaccinated, the vaccine reduced cases of infection by more than a third.
Health experts note that there is also a protective effect for people who vaccinated people become intimate with, because those who are vaccinated will not spread the virus to sexual partners.
Who should get the vaccine?
The HPV vaccine is currently approved by the F.D.A. and recommended by the C.D.C. for people up to age 26. Some experts say this recommendation is based on studies showing that the prevalence of HPV infection in women decreases after age 25. It may be possible for older women to derive some degree of protection from the vaccine, some experts say. Because the vaccine is most effective before people become sexually active, health experts recommend that girls and boys get vaccinated at age 11 or 12. As of last fall, C.D.C. guidelines said that children ages 11 to 14 need only two doses of the vaccine, given at least six months apart. Those receiving the vaccine between ages 15 and 26 should adhere to the previously-used regimen of three doses over a period of six months. The C.D.C. says that even if young people have already had sex before they get the vaccine, it can still provide some protection.