Vaccine Against Cervical Cancer Virus is Effective for More than Four YearsKey Words
Cervical cancer, human papillomavirus (
HPV), prevention, vaccine. (Definitions of many terms related to cancer can be found in the Cancer.gov Dictionary.)
Summary
An experimental vaccine that protects against two types of a virus that can cause cervical cancer remained highly effective for up to 4.5 years and caused very few adverse effects, an international team of researchers reports.
Source
The Lancet, published online April 6, 2006; in print April 15, 2006 (see the journal abstract)
(Lancet. 2006 Apr 15;367(9518):1247-55)
Background
Human papilloma viruses (HPV) are extremely common sexually transmitted infections. In more than 90 percent of cases, the infections are harmless and go away without treatment. However, certain types of HPV increase women’s risk for cancer of the cervix (the neck of the womb). Two types (HPV-16 and HPV-18) cause about 70 percent of all cervical cancers. About a dozen other HPV types are involved in most other cases of the disease.
Although most HPV infections do not progress to cervical cancer, infections that persist for many years are more likely to do so. Most cervical cancers develop slowly through a series of abnormal changes in the cells of the cervix. Regular
Pap tests can detect these changes and the abnormal tissue can be removed, preventing it from ever developing into cancer. Pap tests are not 100 percent accurate, however, and many women do not have regular tests.
It is estimated that in 2006 more than 9,000 women in the United States will be diagnosed with cervical cancer and about 3,700 will die of the disease. Worldwide, about 270,000 women die of cervical cancer each year.
Research is underway to develop a safe and effective vaccine to prevent infection with cancer-causing types of HPV. This study involved one of two experimental vaccines that are currently in development.
The Study
Researchers followed young women (average age 23) who had received three doses of either an experimental HPV vaccine or a placebo between 2000 and 2003 while participating in an earlier study by the same researchers. The earlier study showed that the experimental vaccine prevented most infections with HPV-16 and HPV-18, the two types of HPV that cause most cases of cervical cancer (see the journal abstract).
The initial study followed 1,113 women for about two years. The current, follow-up study extended the follow-up period to 4.5 years for a subgroup of 776 women.
Both studies were supported by GlaxoSmithKline Biologicals, maker of the experimental vaccine used. The studies were conducted in the United States, Canada, and Brazil. The lead investigator for both studies is Diane M. Harper, M.D., of Dartmouth Medical School in Lebanon, New Hampshire.
Results
More than 98 percent of the women who had been vaccinated continued to have antibodies against HPV-16 and HPV-18 in their blood throughout the extended follow-up period - a strong sign that the vaccine remained effective and was preventing them from becoming infected with those strains of HPV.
In addition, none of the women in the vaccine group developed any abnormal changes in cells of the cervix of the type caused by HPV-16 or HPV-18. By contrast, women in the placebo group developed many precancerous abnormalities in the cells of the cervix.
The vaccine also partly protected many women from two other strains of HPV, HPV-45 and HPV-31, which are the third and fourth most common HPV types associated with cervical cancer. None of the women who were vaccinated reported any serious side effects from the medication.
Comment
This study, like previous studies of HPV vaccines, did not directly show that vaccination reduces the occurrence of cervical cancer. Such a study would take between 10 and 20 years to complete and would be unethical, explains John T. Schiller, Ph.D., of the National Cancer Institute’s Center for Cancer Research.
“Because cervical cancer can be almost completely prevented using current procedures - including Pap tests, HPV testing, follow-up diagnostic testing of cervical abnormalities, and surgery to remove premalignant lesions - no one is going to do a follow-up study with a cervical cancer endpoint,” says Schiller.
Harper and her co-authors write that their findings “set the stage for the widescale adoption of HPV vaccination for prevention of cervical cancer."
No HPV vaccine is currently approved for marketing in the United States. GlaxoSmithKline, the maker of the vaccine used in this study, is expected to apply for approval of the vaccine by the U.S. Food and Drug Administration (FDA) in 2006. Merck, the maker of a second experimental HPV vaccine, has already applied to the FDA for approval of its product.
“An HPV vaccine will not replace the Pap test or eliminate all HPV infections,” notes Schiller. Also, although a vaccine may prevent new HPV infections, it will not make pre-existing persistent HPV infections go away.
Schiller adds that because women often get HPV infections soon after they initiate sexual activity, a vaccine will be most effective if it is given to young women before they begin to have sex.
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