The phase II study evaluated the efficacy of Gardasil in preventing infection from the types of human papillomavirus (HPV) responsible for 70% of all cases of cervical cancer and 90% of all cases of genital warts.
The primary endpoint of the study was to assess the efficacy of the investigational vaccine in reducing the combined incidence of persistent HPV 6, 11, 16, and 18 infections and related diseases, including cervical precancers, cervical cancer, and/or genital warts.
Over the two and a half years of follow-up after vaccination, Gardasil reduced the combined incidence of persistent infection from HPV 6, 11, 16, or 18 and related genital disease including new cervical precancers and genital warts by 90% compared with placebo among women who were naive to the relevant HPV types at baseline.
However, adverse events related to the injection site were higher among those who received Gardasil compared with placebo recipients. The most common injection site and systemic adverse events were pain and headache, respectively. None of the subjects who received the investigational vaccine discontinued the study due to an adverse experience.
“HPV types 6 or 11 are not linked to cervical cancer, but they can cause abnormal Pap smears, which then lead to additional tests – and unnecessary worries about cancer,” said Dr Eliav Barr, senior director of clinical research at Merck Research Laboratories, and a co-author of the study.
“Gardasil was purposefully designed to target the HPV types most commonly associated with cervical cancer, as well as the types that cause genital warts and many abnormal Pap smears, to reduce the burden from HPV infection as much as possible.”