Cervarix has been shown to be 100% effective in preventing infection with HPV strains 16 and 18, which together cause about 70% of cervical cancer cases. Researchers in a 2006 study published in the online edition of the Lancet also found that Cervarix prevented infection with HPV strains 31 and 45, which together with strains 16 and 18, cause more than 80% of cervical cancer cases.
The Australian Therapeutic Goods Administration in June approved the vaccine for girls and women ages 10 to 45, and the European Committee for Human Medicinal Products last month recommended the vaccine for sale and marketing in the European Union. FDA has granted a standard 10-month review of the vaccine and most likely will take action on GSK's application in January 2008, according to analysts at Evolution Securities.
For the study, Allan Hildesheim, a senior investigator at NCI, and colleagues between June 2004 and December 2005 enrolled 2,189 women ages 18 to 25 in Costa Rica who tested positive for HPV DNA at the time of enrollment. About half of the women in the study were given Cervarix and half were given the hepatitis A vaccine.
According to the findings, 33.4% of the women who received Cervarix had cleared HPV infection after six months, compared with 31.6% in the control group (Hildesheim et al., JAMA, 8/15). After one year, 48.8% of women who received Cervarix had cleared the infection, compared with about 49.8% who had not received the vaccine. The study also found that most HPV infections, regardless of the strain, clear spontaneously over a period of six months to two years.
"You should not get [Cervarix] because you want to treat an existing infection," Hildesheim said. He added, "The question that has not yet been answered is whether protecting [a woman] from reinfection of a virus that she has previously been infected with, and successfully cleared, will in fact reduce that woman's risk of getting cervical precancer and cancer".
GSK spokesperson Liad Diamond, said the results of the study are "completely expected." GSK and Merck, which makes the HPV vaccine Gardasil, said their vaccines are not intended to treat existing infections, adding that the study's findings confirm their companies' research.
Source: Kaiser Family Foundation