By Dennis Thompson
WEDNESDAY, June 19 (HealthDay News) -- Vaccination against the cancer-causing human papillomavirus (HPV) is proving highly effective in reducing the spread of the sexually transmitted virus among young women, new research shows.
The rate of new infections with strains of HPV targeted by the vaccine have dropped by 56 percent among females aged 14 to 19 since the first vaccine was approved in 2006, report researchers at the U.S. Centers for Disease Control and Prevention.
According to the CDC, HPV infection is known to be the major cause of cervical cancer, and has also been strongly linked to vulvar, vaginal, penile, anal, and certain throat/oral cancers.
The new findings "are striking results, and I think they should be a wake-up call that we should increase vaccination rates, because we can protect the next generation of adolescents and young girls against cancer," CDC director Dr. Tom Frieden said in a press conference held Wednesday.
The findings are published in the June issue of The Journal of Infectious Diseases.
Each year in the United States about 19,000 cancers caused by HPV occur in women, with cervical cancer being the most common. Virtually all cases of cervical cancer are caused by HPV, and just two HPV subtypes, 16 and 18, are responsible for seven out of every 10 cervical cancers.
About 8,000 cancers caused by HPV occur each year in men in the United States, most commonly being throat cancer.
The decline in HPV infections among girls is actually higher than had been expected, indicating that "herd immunity" may have taken effect as more girls receive the vaccine, study lead author Dr. Lauri Markowitz said at the press conference.
Herd immunity occurs when widespread vaccination shrinks the pool of infected people to the point that it becomes less likely that a person can catch the disease from someone else. In this type of scenario, "even people who aren't vaccinated will have some protection due to the vaccination program," Markowitz said.
Another possible reason for the better-than-expected results could be that the vaccine is so effective that a girl receives protection from HPV even if she receives only one or two shots out of the full recommended three-dose series of vaccination.
Whatever the reason, the new statistics are "great news," according to Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, La. "I think every young woman should have the opportunity to have this vaccine. That's what I've been telling people for however long the vaccine has been available."
HPV is highly infectious. In fact, about 79 million Americans, most in their late teens and early 20s, are thought to be currently infected with HPV, and each year about 14 million people become newly infected.
The study was based on data from the CDC's National Health and Nutrition Examination Survey. It compared HPV infections in teenage girls from 2003 to 2006 (before the start of the United States' HPV vaccination program) against infections that occurred from 2007 to 2010, after girls began receiving the vaccine.
The CDC team showed that infections by the HPV types covered by the vaccine fell dramatically -- from 11.5 percent in the pre-vaccine era to 5.1 percent post-vaccine.