The prevalence of human papillomavirus (HPV) among teenage girls in the United States has been reduced by nearly two-thirds due to a vaccine introduced 10 years ago, a new report revealed.

Even among women in their early 20s, a group which has lower vaccination rates, the most fatal strains of HPV have been lowered by more than a third.

The report examined the prevalence of HPV among women and girls of different age groups during 2003 to 2006. Researchers also looked at the prevalence in the same age groups in 2009 to 2012.

By then, cases of HPV covered by the vaccine decreased by 64 percent in girls who are 14 to 19 years old. In women aged 20 to 24, the prevalence declined by 34 percent.

"The vaccine is more effective than we thought," said public health expert Debbie Saslow.

The statistics are considered as a "welcome energizer" in the struggle to encourage HPV vaccination in the country, experts said. Despite the vaccine's proven efficacy, however, immunization rates remain low. Only about 40 percent of girls and 20 percent of boys between 13 to 17 years old are immunized against the virus.

The New York Times pointed out that this may be because of the implicit association of the HPV vaccine with adolescent sexual activity rather than its real purpose -- cancer prevention. Additionally, only the District of Columbia and Virginia, Rhode Island requires the vaccine.

The vaccine, which is called Gardasil, works against four strains of HPV. The strains cause almost all cases of cervical cancer. HPV also causes cancers of the mouth, throat, and anus, as well as genital warts.

About 14 million Americans are infected with HPV every year. The majority of these patients will clear the virus. Unfortunately, some strains still persist. What's more, the American Cancer Society estimates that about 4,120 women will die of cervical cancer this year.

However, many still oppose the HPV vaccination. Some hold anti-vaccine sentiments, while some say it could encourage teenagers to have unprotected sexual activity.

"Showing the effectiveness of a vaccination program may help to convince doubters," said Johannes Bogaards of the National Institute for Public Health and the Environment in the Netherlands, who was not involved in the new study.

Simon Barton of Imperial College London meanwhile believes the new study may assuage worries that the vaccine will encourage risky sexual behavior.

The study will be featured in the journal Pediatrics.

Photo: Pan American Health Organization | Flickr