By Alan Mozes

HealthDay Reporter

THURSDAY, April 18 (HealthDay News) -- In the five years since launching a nationwide human papillomavirus (HPV) vaccination program among girls between the ages of 12 and 26, Australia has seen a huge drop in the number of cases of genital warts, new research reveals.

Among Australian girls in the targeted age range for vaccination, the country saw genital wart cases plummet by 59 percent within just the first two years of the program's launch in 2007.

By aggressively vaccinating girls against HPV (which is responsible for 90 percent of genital wart diagnoses), Australia appears to have offered considerable protection not just to its female population but also its men as well.

How? Researchers point to a phenomenon known as "herd immunity," whereby the immunity acquired by a certain segment of the population -- in this case, women -- ends up protecting an unvaccinated segment of the population (men).

In the same timeframe Australia has seen a 39 percent drop in genital wart cases among heterosexual men as well.

"All indications are that the program has been an overwhelming success," noted study author Dr. Basil Donovan, who heads the sexual health program at the Kirby Institute of the University of New South Wales, in Sydney.

"But we won't be certain until HPV-related cancers [also] start dropping," he added, explaining that while genital warts tend to appear roughly three months following infection with HPV, "the incubation period from HPV infection to HPV-related cancer is typically at least 20 to 30 years."

HPV-associated cancers include cervical, penile, anal and throat cancers, according to the U.S. Centers for Disease Control and Prevention.

Donovan and his colleagues published their findings in the April 18 issue of the BMJ.

To explore the impact of HPV immunization efforts in the Australian context, the authors analyzed data collected from eight different sexual health service organizations covering a period from 2004 to 2011.

Collectively, the organizations had seen nearly 86,000 first-time patients in that timeframe, of whom about 9 percent were diagnosed with genital warts.

By comparing the pre-vaccination period of 2004 to mid-2007 with the vaccination period of mid-2007 through the end of 2011, the team found a remarkable plunge in genital wart rates.

Among girls under the age of 21, that drop amounted to nearly 93 percent, while among those between 21 and 30 a decline of almost 73 percent was observed.

And while no appreciable genital wart rate drop-off took place among women or men over the age of 30, among men under 30 a notable dip was observed. Specifically, among heterosexual men below 21 the drop amounted to almost 82 percent, while among those between 21 and 30 genital wart rates fell by more than 51 percent.

But is the Australian experience translatable to other countries now engaged in various types of HPV vaccination programs?

Donovan said that how well other countries will fare in efforts to dampen genital wart rates will depend on the degree of public acceptance when it comes to HPV immunization efforts.

"There was little resistance to the HPV vaccine in Australia," he noted by way of explaining the program's success. By contrast, he suggested that the American public health effort -- which he characterized as "fractured" -- may very well produce less optimistic results, given the widespread controversy and reluctance to vaccinate that arose when the prospect of immunizing young girls was first proposed.

But in other countries, where the debate has been more muted, Donovan sees better prospects. "As the U.K. is achieving vaccine coverage rates at least as high as Australia," he said, "I would be certain that they will soon be reporting comparable drops in disease."

Commenting on the report, Dr. Jocylen Glassberg, an obstetrician/gynecologist at Scott and White Healthcare in Round Rock, Texas, said that "the take-home message is the vaccine is obviously working."

"It will take many more years to see the same decline in cervical cancer rates due to the naturally slow progression of that disease process," she said. "But the vaccine works. The fact that genital wart rates were virtually zero after such a short time in women and men, even in a program just aimed at vaccinated women, is a phenomenal result."

On that note, Glassberg pointed out that most vaccines do not offer similar levels of protection. "Flu vaccines keep 80 percent or so at bay," she explained. "This is almost 100 percent."

So, "aggressively educating the public should be key in the U.S.A. as well," she concluded. "And getting the vaccines covered in young women, and men, as a medical benefit could lead to a near eradication of genital warts here as well."

In the United States, the vaccines Gardasil and Cervarix are used to prevent HPV infection and are highly effective, according to the U.S. National Institute of Allergy and Infectious Diseases.

More information

To learn more about HPV and genital warts, visit the U.S. National Institute of Allergy and Infectious Diseases.