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Human papillomavirus (HPV) types 16 and 18 cause about 70% of cervical cancer worldwide. At least one vaccine is already available, and others are in development, including a bivalent vaccine against HPV types 16 and 18 developed by GlaxoSmithKline. The vaccine, which is a virus-like particle plus an adjuvant, is being tested in a phase III trial, which includes more than 18000 women from 14 countries. So far it seems to work.work.
In an interim analysis, three doses of the vaccine prevented more than 90% of cases of cervical intraepithelial neoplasia grade 2 or higher in adolescents and young women who were uninfected at the time of vaccination (efficacy 90.4%, 95% CI 53.4% to 99.3%). It also seemed to protect them against other oncogenic HPV types, preventing between 32% and 60% of infections with types 31, 45, and 52. Almost all the women given the vaccine seroconverted, generating an antibody response well in excess of the response seen in naturally occurring HPV infections. Controls were vaccinated against hepatitis A.
These results look promising, says a linked commentary (doi: 10.1016/S0140-6736(07)60947-7). But researchers need to keep a close eye on side effects. The interim data contain a hint that spontaneous abortions many be more common among women given the vaccine (absolute risk difference 2.5%, 95% CI −0.5% to 5.5%, P=0.106).