The human papillomavirus vaccine strongly and consistently protects against genital warts - one of the more common sexually transmitted infections - as well as the lesions causing cervical cancer, according to an international study published Wednesday in the British Medical Journal.
The research involved about 17,500 women in North America, Latin America, Europe and Asia Pacific. All were 16 to 26 years old with fewer than four sexual partners, and all had enrolled in two studies from 2001 to 2003.
This has been a hallmark, which is good news for both vaccines. Prof. Eduardo Franco, McGill University
One group of women was given a placebo. The other group received the vaccine for four strains of HPV: 6, 11, 16 and 18. Strains 16 and 18 cause more than 70 per cent of cervical cancer cases while strains 6 and 11 cause about 90 per cent cases of genital warts.
For these strains, the vaccine prevented genital warts by 99 per cent and low-grade lesions by 96 to 100 per cent - for up to three and a half years of follow-up.
"It is prolonged and almost complete protection," says lead author Joakim Dillner, a professor of virology and molecular epidemiology at Sweden's Lund University.
Prof. Dillner and his co-authors say the findings should be a relief to women - and health-care costs.
"When a Pap smear is not normal, it produces anxiety. Low-grade lesions can be related to a cancer-causing virus, but they can also be caused by benign viruses. It's not possible to tell, so all the women with a light abnormal Pap smear will need follow-up, which causes distress [for the patient]and health-care costs for society."
There are more than 200 strains of HPV, and they are responsible for about 500,000 cases of cervical cancer a year globally. About 30 million women and men suffer from anogenital warts or low-grade cervical growths each year. About 1,300 Canadian women were diagnosed with cervical cancer in 2009, and there were 380 deaths attributable to the condition, according to the Canadian Cancer Society.
The studies were funded by Merck & Co. Inc., which makes Gardasil, one of two competing HPV vaccines approved by Health Canada. (The other is Cervarix, a product of GlaxoSmithKline Inc.)
The large sample size of the studies and nearly four years of follow-up make them significant, said Eduardo Franco, a professor of epidemiology and oncology director in the division of cancer epidemiology at McGill University.
"This has been a hallmark, which is good news for both vaccines," Prof. Franco said.
In Canada, HPV vaccines are recommended for all girls and women aged 9 to 26, and the vaccine is offered to preteen and teenaged girls free in school-based programs in all 13 provinces and territories.
The vaccines can also offer protection against cervical cancer to women who are sexually active and even those who have had abnormal Pap tests.
Prof. Franco noted that both Merck and GSK are now looking at vaccinating boys and women over 40 years of age. Still, he argued that screening is the supreme weapon, especially for women who have already acquired the infection. "Screening will continue because these two vaccines should be called first-generation vaccines at this point. They do not yet protect against all the HPV genotypes that cause cervical cancer."
He added: "The good news is that there are technologies on the horizon. They're going to make screening far more efficient and less frequent, so the annual Pap test is going to disappear eventually. We're going to have better tools to screen every four or five years. Women won't have to be as captive to their family doctors as they used to be."