The findings represent the longest follow-up yet of an experimental human papilloma virus (HPV) vaccine, which has the potential to dramatically lower deaths from cervical cancer.
Two such vaccines are poised to hit the market in the U.S., pending approval by the FDA. The agency is expected to rule on Merck's vaccine — called Gardasil — early in June.
A spokesman for GlaxoSmithKline tells WebMD that the company plans to seek FDA approval for its HPV vaccine — Cervarix — by the end of the year.
"With fast-track status, if all goes well, we could have [approval] within six months," says Phillippe Monteyne, who heads global vaccine development for the company.
100 Percent Protection
The study included 800 women who were vaccinated with either three doses of Cervarix or a placebo.
In November 2004, researchers reported that the vaccine was 100% effective in preventing persistent infection with the two HPV strains that cause about 70 percent of cervical cancers — HPV-16 and HPV-18.
In a follow-up, published in the latest issue of The Lancet, they reported that the women given the vaccine continued to be protected 4½ years after receiving the last dose of the vaccine.
The women were also protected against two other HPV strains that have also been associated with cervical cancer — HPV 45 and HPV 31. This cross-protection occurred even though the vaccine was not designed to target these strains.
About half a million cases of cervical cancer are diagnosed worldwide each year, and an estimated 280,000 women — mostly in developing countries — die from the disease.
Researchers estimate that if all eligible women got the vaccine, it would reduce the worldwide incidence of cervical cancer by almost 70 percent.
"This is a very exciting time," says Diane M. Harper, M.D., MPH, who led the study team. "We haven't had an advance like this in cancer care or in women's health for 50 years. This has tremendous potential."
There are still many unanswered questions — most notably who will get the vaccine, when they will be vaccinated and which vaccine they will get.
The GlaxoSmithKline vaccine protects against cervical cancer alone, while the Merck vaccine also targets two HPV viruses that cause genital warts.
But Harper says her findings suggest that the GlaxoSmithKline vaccine may protect women against cervical cancer longer than its competitor.