Ongoing evaluation of a phase II trial of a human papillomavirus vaccine, developed to prevent cervical cancer, shows that the vaccine continues to protect against HPV types 16 and 18 at five and a half years into the study, according to researchers from the University of Louisville.
Their findings also show that the vaccine offers significant cross-protection for HPV types 45 and 31.
The study follows 1113 women between the ages of 15 and 25 in North America and Brazil randomized to receive three doses of either the vaccine or the control. The vaccine, made by GlaxoSmithKline, which funded the study, is designed to protect against two strains of HPV, types 16 and 18, which together are thought to cause nearly 72 percent of all cases of cervical cancer.
At over five years into the study?s follow-up, the researchers found that approximately 98 percent of subjects still maintained protection against HPV types 16 and 18. Regardless of HPV status, the vaccine also appears to prevent most occurrences of cervical intraepithelial neoplasia lesions ? abnormal, precancerous cell growths found in the cervix.
They also found that the vaccination offered significant protection against genetically similar viruses. They determined the vaccine to be 88 percent effective against HPV type 45 and 54 percent effective against HPV type 31.
“Overall, it is not a surprise that the vaccine offers protection against additional types of human papillomavirus, as they are all related genetically,” said Stanley Gall, M.D., professor at the University of Louisville. “However, as you get genetically farther from types 16 and 18, you would expect to see less cross-protection.”
According to Dr. Gall, effective preventative treatment with the vaccine will depend on the long-term and broad protection the vaccine can offer against cancer-causing HPV types.