Human papillomavirus (HPV) is the most common sexually transmitted infection in the U.S. and a principal cause of cervical cancer, but a new vaccine has blocked its spread.

Introduced in 2006, the HPV vaccine has cut the infection rate among girls aged 14 to 19 by 50 percent in only four years, according to 2010 data published in June in The Journal of Infectious Diseases. These results were achieved despite the fact that only about one-third of teenage girls have been vaccinated with the full course of three doses.

By blocking the spread of infection, the vaccine is preventing cancer and saving lives.

“This is an anti-cancer vaccine,” said Centers for Disease Control (CDC) Director Thomas Friedan. He cited data showing about 79 million Americans are currently HPV-infected, about a quarter of the population. Infection rates are highest among teens and 20-somethings, the nation’s most sexually active cohorts. Each year, another 14 million people become infected. The virus causes about 19,000 new cancers in women every year. About 8,000 men also develop (mostly throat) cancer due to HPV. The disease annually kills about 4,000 Americans.

By vaccinating girls and boys before they become sexually active, much of this cancer can be avoided. Excited about the progress so far, health officials hope to continue the early success by increasing the rate of vaccination among girls and boys.

Why the low rate of vaccination?

Other nations have significantly higher HPV immunization rates than the U.S. The stigma that surrounds sexually transmitted disease in the U.S. may affect the American rate. HPV is acquired only through sexual transmissions. As a result, some parents worry that in guiding their children to get the vaccination, they will encourage promiscuity.

Other parents are concerned about possible serious side effects . While no evidence of such an association exists, officials worry because, a decade ago, a significant backlash against immunization developed among some parents fearful that childhood vaccines might be the cause of their children’s autism. Despite extensive investigations, no link was ever found.

The HPV vaccine is delivered by injection, a procedure that often produces soreness or a low fever whatever the medication. However, despite more than 100 million HPV doses worldwide and 26 million in the U.S., doctors at the CDC have found no pattern of serious adverse events.

Why the initial success?

Health officials offered various explanations for the evident progress against the virus despite the limited rate of vaccination.

Some cited herd immunity, the phenomenon in which any significant increase in vaccinated people reduces the chances that unvaccinated people will get the disease (since, aggregately, a larger portion of their sex partners will be vaccinated and not carry the virus). Others explained that, unexpectedly, even one dose of the vaccine seems to have some effect, and about half of teenage girls have received at least one dose. Also, some researchers speculated that many of the girls and women who self-selected for the vaccine may be more sexually active than those who did not, so those who might have contributed most to the spread of the disease are not doing so.

Appropriate care

Two vaccines are approved. Cerarix (made by GlaxoSmithKline) protects against two HPV strains that cause 70 percent of cervical cancers. It is approved for girls and women aged 10 to 25. Gardasil (Merck) is effective against four strains of HPV, including the two that cause most cervical cancers and two that cause 90 percent of genital warts. It is approved for males and females aged 9 to 26 and recommended for all girls aged 11 and 12. Recently, the Advisory Committee on Immunization Practices recommended vaccination of boys aged 11 and 12. Twenty-two states currently require HPV vaccination (in some states, religious or other exceptions are allowed), and measures to require its use have been introduced in another 20 states.

Contact your health and welfare fund office to determine what benefits are provided for HPV vaccination. Parents can best protect their children from this cancer risk by asking their doctors to vaccinate.

[Steve Clark]