The incidence of genital warts declined by more than 90% in adolescent and teenage girls in the first 4 to 5 years after introduction of the human papillomavirus (HPV) vaccine in Australia, investigators reported.

Genital warts occurred more than 70% less often among women 21 to 30, as compared with the 3 to 4 years before the vaccine became available. The reductions in wart incidence among girls and women were accompanied by 50% to 80% decreases in the incidence of genital warts among heterosexual boys and young men.

No decline in wart frequency was seen in heterosexual women or men older than 30, Basil Donovan, MD, of the University of New South Wales in Sydney, and co-authors reported online in BMJ.

Action Points The incidence of genital warts declined by more than 90% in adolescent and teenage girls in the first 4 to 5 years after introduction of the human papillomavirus (HPV) vaccine in Australia.

Note that the reductions in wart incidence among girls and women were accompanied by 50% to 80% decreases in the incidence of genital warts among heterosexual boys and young men although no decline in wart frequency was seen in heterosexual women or men older than 30.

"In 2011 no genital wart diagnoses were made among 235 women under 21 years of age who reported prior human papillomavirus vaccination," the authors noted. "The significant declines in the proportion of young women found to have genital warts and the absence of genital warts in vaccinated women in 2011 suggests that the human papillomavirus vaccine has high efficacy outside the trial setting. Large declines in diagnoses of genital warts in heterosexual men are probably due to herd immunity."

The study provided a glimpse of the impact of HPV vaccination in a real-world community setting as opposed to a clinical trial.

"It actually generated data consistent with what we hoped and predicted would happen," said Greg Poland, MD, of Mayo Clinic in Rochester, Minn. "It showed in a large study that [the vaccine] worked and it worked fabulously."

It is probable that the results are readily applicable to the U.S. and other countries that have introduced HPV vaccination, he added. In particular, the results should reassure girls, young women, and parents that the vaccine is safe, effective, and does not promote promiscuity, which has been a concern to some people.

Poland was not involved in the study.

In 2007 Australia implemented one of the first nationwide HPV vaccination programs for girls and young women. The nationally funded program provides free vaccination to girls 12 to 13 in schools, and a vaccination "catch-up" program from 2007 to 2009 offered vaccinations to girls 13 to 18 and women 18 to 26.

The vaccination program included a surveillance network to monitor the effect of the vaccine on the incidence of genital warts in patients seen at sexual health services clinics. The first report from the program, 2 years after its implementation, showed a 59% reduction in wart incidence among vaccine-eligible women 12 to 26 and a 39% decrease in heterosexual men of the same age.

Donovan and colleagues updated the population effects of the vaccination program for 2007 to 2011.

From 2004 to 2011, 85,770 native-born Australians made initial visits to eight sexual health services. Evaluations showed that 7,686 (9.0%) of the patients had new diagnoses of genital warts (2,394 women and 5,292 men). From 2004 to 2007 the proportion of women with genital warts increased from 8.9% to 9.6% and then decreased to 2.7% by 2011. Among men, the rate declined from 12.8% to 11.7% during the first years, followed by a decrease to 7.4% by 2011.

The largest decline in genital-wart incidence occurred among women younger than 21. From a peak of 11.5% in 2007, the incidence of genital warts decreased to 0.85% by 2011, representing a reduction of 92.6% (P<0.001). Among women 21 to 30, the incidence of genital warts declined slightly from 12.5% in 2004 to 11.3% in 2007 before falling to 3.1% by 2011, a 72.6% decrease (P<0.001). The incidence did not decline significantly among women older than 30.

Rates of genital warts among heterosexual men seen at the sexual health services facilities increased by 68% (7.2% to 12.1%) from 2004 to 2007 (P<0.01) but declined by 82.8% to a low of 2.2% in 2011 (P<0.001). The incidence not changed significantly over time among men 21 to 30 or those older than 30.

Authors of a related editorial said the study showed a "remarkable reduction" in genital warts among women younger than 21 and predicted that "near eradication of genital warts in young Australian women will probably have a major impact on the costs of sexual healthcare."

"It remains to be seen whether we will see similar dramatic reductions in HPV-16 and HPV-18 associated diseases, such as cervical cancer, vulval cancer, other anogenital cancers, and head and neck tumors as a result of national vaccination programs," wrote Simon Barton, MD, of the Chelsea and Westminster Foundation Trust in London, and Colm O'Mahony, MD, of the Countess of Chester Trust in Chester, England.

"This is likely given the reported evidence of the vaccines. It is hoped that future vaccines will protect against other HPV types, such as types 31 and 45, which are also involved in the genesis of genital cancer. Countries should carefully explore whether it is economically feasible to vaccinate young men."