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International studies show high efficacy for HPV vaccine

June 01, 2007

A new vaccine aimed at preventing cervical cancer is nearly 100 percent effective against the two types of the human papillomavirus (HPV) responsible for most cases of cervical cancer—strains 16 and 18. Results of an international meta-analysis study of the vaccine are published in the June 1 issue of the journal Lancet.

In the current and largest study to date, researchers combined and analyzed the data from four randomized trials that involved 20,583 women ages 15 to 26 from more than two dozen countries across Europe, North America, Latin America and Asia. Participants were randomly assigned to receive the HPV vaccine or placebo and followed for an average of three years.

Researchers found that the prophylactic administration of the vaccine was highly effective in preventing pre-malignant changes of the cervix, also known as cervical dysplasia.

"This is a much larger combined study that shows 99 percent efficacy, a clear reduction of pre-cancerous cervical lesions. We demonstrated significant protection against serious HPV-related diseases, including high-grade cervical pre-cancers, in women not previously exposed to the relevant HPV types targeted by the vaccine," says Kevin Ault, MD, associate professor of obstetrics and gynecology at Emory University School of Medicine, one of the authors of the study and a key researcher in the development of the vaccine.

HPV strains 16 and 18 are responsible for about 70 percent of all cases of cervical cancer. In clinical trials the vaccine, manufactured by Merck under the name Gardasil, also demonstrated a high efficacy rate in protection from HPV types 6 and 11, which together cause about 90 percent of all cases of genital warts. All four types cause a large number of abnormal Pap test results and low-grade cervical lesions.

Cervical cancer is the second most common cause of cancer deaths in women worldwide, accounting for about 240,000 deaths each year. In 2007 experts predict cervical cancer will strike an estimated 11,000 women in the United States and nearly half a million women worldwide. Every day in the United States ten women die from cervical cancer, says Dr. Ault.

"Thanks to the results of this meta-analysis and a previous publication in Lancet, we now have data on three more rare cancers -- adenocarcinomas in situ of the cervix, as well as vulvar and vaginal cancer. All these female cancers are caused by HPV and can be successfully prevented with the HPV vaccine."

According to estimates from the Centers for Disease Control and Prevention (CDC) more than 20 million men and women in the United States are infected with HPV, and more than six million new infections are reported each year, making it the most common sexually transmitted disease in the nation.

"Nearly all sexually active people are going to get exposed to the virus sometime during their lives," says Dr. Ault. For most people, HPV causes no complications and goes away on its own. However, in some cases, if left untreated, certain high-risk types of HPV can lead to cervical cancer.

"The goal of the study was to see if we could prevent precancerous cases and the results of this combined analysis show near 99 percent effectiveness. Everyone who gets cancer goes through a pre-cancerous stage," says Dr. Ault. "There are about 50 to 60 million pap smears performed each year in the United States, and about seven percent are abnormal. We spend about 3 billion dollars each year to find and treat these pre-cancerous stages caused by some type of HPV."

Gardasil was approved by the U.S. Food and Drug Administration last year for use in females 9 to 26 years of age. While controversy has been raised about giving pre-adolescent girls a vaccine for a sexually transmitted disease, Dr. Ault argues, "young women, young girls make very good immune responses to this vaccine, so that will enhance their protection. Widespread immunization with the HPV vaccine along with continued screening will help decrease the burden of cervical cancer and other HPV-related diseases," he says.

Emory University