By Ed Susman
TAMPA, Fla -- March 14, 2008 -- Vaccination against human papillomavirus (HPV) types 16 and 18 appears to sustain effectiveness for at least 6.4 years, researchers reported here at the Society of Gynecologic Oncologists (SGO) 2008 Annual Meeting on Women's Cancer.
The vaccine has previously been demonstrated to be 100% effective against HPV 16/18 persistent infections as well as cervical intraepithelial neoplasia (CIN) 1 and CIN2, noted investigator Diane Harper, MD, Associate Professor of Community and Family Medicine and Associate Professor of Obstetrics and Gynecology, and Adjunct Associate Professor of Women's and Gender Studies, Dartmouth College, Hanover, New Hampshire.
"Every cost-effectiveness analysis that we have seen indicates that the most important factor is the duration of effectiveness of the vaccine," Dr. Harper said in her late-breaking plenary presentation on March 10. "We have asked the women in this study to continue follow-up for 9.5 years," she said.
"We have seen high and sustained seropositivity for both [HPV] 16 and [HPV] 18 at levels equal to or greater than 98% for both types," she said.
She demonstrated that 7 months after vaccination, seropositivity against HPV type 16 reached 100%. Seropositivity dipped to 99% after 25 months, but then rebounded to 100% and stayed between those levels until the 76-month follow-up, when seropositivity was again measured at 100%.
The results were similar for seropositivity against HPV type 18, maintaining seropositivity from month 7 through month 39. The seropositivity dipped briefly to 98% but rebounded to 100% after 76 months.
Dr. Harper also reported that sustained neutralising antibodies after 5.5 years of follow-up remained at 10 times the level believed to be required to prevent infection with HPV types 16 and 18.
Although HPV types 45 and 31 were not part of the vaccine, the inoculation still appeared to provide a 78% reduction in risk of infection with type 45 and a 60% reduction in infection with type 31. "[HPV] types 16, 18, 45, and 31 are responsible for 80% of squamous carcinoma and more that 80% of adenocarcinoma," Dr. Harper added.
The incidence of CIN2 cases caused by any types of HPV infection in the trial participants occurred in 5 of 505 women who received the active vaccine and in 12 of 497 women who received placebo injections, a 72% reduction in events.
After 6.4 years there were no cases of CIN1-positive infection caused by HPV types 16 or 18 among women who received the active vaccine, compared with 15 cases among the placebo group, Dr. Harper said.
After 6.4 years, there were no cases of CIN2-positive infection caused by HPV types 16 or 18 among vaccinated women, compared with 9 women in the placebo group, she said.
Vaccination did not appear to have any negative impact on pregnancy or delivery, Dr. Harper said. About 80% of 130 women who received the active vaccine had normal deliveries with 1 abnormal birth, compared with 68.7% normal births and 5 abnormal births in 131 women who were inoculated with placebo.
Funding for the studies with the HPV vaccine against types 16 and 18 was provided by GlaxoSmithKline.
[Presentation title: High and Sustained Protection Up to 6.4 Years With GSK's AS04 Advanced Cervical Cancer Vaccine. Abstract LB1]
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