Within its first four years, the human papillomavirus (HPV) vaccine reduced by half the prevalence of the most insidious strains of the sexually transmitted virus among teenage girls, notwithstanding the vaccine's lack of widespread use, The New York Times reports. Called Gardasil, the vaccine was introduced in late 2006 as a routine, recommended, three-dose vaccine for girls 11 to 12 years old, with a catch-up vaccination recommended for young women 13 to 26 years old. By 2010, only a third of 13- to 17-year-old girls had received all three shots.

Researchers at the Centers for Disease Control and Prevention (CDC) studied the prevalence of the four most carcinogenic strains of the virus. (HPV can cause cervical cancer.) The team compared data on the virus's prevalence between the pre-vaccine period of 2003 and 2006 with the post-vaccine release period of 2007 to 2010. All told, they studied cervicovaginal swab samples taken from 4,150 women and girls between the ages of 14 and 59 during the earlier time period and 4,253 females during the second period.

Between the two time frames, the prevalence of the four most dangerous strains of HPV dropped from 11.5 percent to 5.1 percent, for a 56 percent rate of decline. And for girls ages 14 to 19, infections with those strains dropped from 7.2 percent in 2006 to 3.6 percent in 2010. There was no significant change in prevalence among the older females studied.

The research also found that a single dose of the vaccine was 82 percent effective at protecting against HPV.

To read the Times story, click here.

To read the journal abstract, click here.