The human papillomavirus (HPV) vaccine Cervarix protects women from infection for longer than six years, new research has found.
The vaccine guards against the two types of HPV (HPV-16 and HPV-18) most commonly associated with cervical cancer.
The study looked at nearly 800 women, aged 15 to 25, with a normal cervical profile and no evidence of HPV infection at the start of the trial. There were 393 women who received the Cervarix vaccine and 383 who received an inactive placebo. Every six months for 6.4 years, the women were tested for HPV DNA.
The researchers found that vaccine efficacy against 12-month persistent infection with HPV-16/18 remained 100 percent during the study period. Vaccine efficacy against incident infection with HPV-16/18 was 95 percent. Antibody concentrations against HPV-16/18 in vaccinated women remained at least several-fold higher than would be found after natural HPV infection, the study authors noted.
Cervarix also protected women against incident infection with HPV-31 and HPV-45, which "are among the types most frequently associated with cervical cancer after HPV-16 and HPV-18, and are responsible for 10 percent of all cervical cancer cases," wrote Dr. Cosette Wheeler, of the Health Sciences Center at the University of New Mexico, and colleagues.
The study was released online Dec. 2 in advance of publication in an upcoming print issue of The Lancet.
"Although further assessment is necessary to confirm long-term vaccine effects, in view of the data from our study, we expect protection to continue for many more years," the researchers concluded.
Cervarix, from GlaxoSmithKline, received U.S. Food and Drug Administration approval in October.