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Vaccine Found to be 100% Effective at Preventing Cervical Cancer (dateline December 15, 2005)

An experimental vaccine has been found to be 100% effective at preventing the most common forms of cervical cancer, according to results of a two-year study. announced by Merck and Co. at the annual meeting of the Infectious Diseases Society of America. The study, which involved more than 12,000 women from 13 countries, showed that the genetically engineered vaccine called Gardasil blocked infection of two common strands of the human papillomavirus (HPV), a common sexually transmitted disease. Merck expects to receive approval by the U.S. Food and Drug Administration (FDA) by the end of the year and begin offering the vaccine to pre-sexually active girls in 2006.

"To have 100 percent efficacy is something that you have very rarely," Dr. Eliav Barr, Merck's head of clinical development for Gardasil, told The Associated Press. The study results were announced in October 2005 by Merck and Co. at the annual meeting of the Infectious Diseases Society of America.

The vaccine works by preventing infection from two forms of HPV, a common sexually transmitted disease that affects both men and women. There are over 80 different strains of HPV and most do not pose any health risks. However, some strains of HPV (in particular, HPV-16, HPV-18, HPV-31, and HPV-45) can cause cellular changes that may lead to cervical cancer in women. The vaccine blocks HPV-16 and HPV-18, which account for about 70% of cervical cancer cases. An estimated 20 million American men and women are carrying HPV.

According to the American Cancer Society, approximately 13,000 women will develop invasive cervical cancer this year, and about 4,100 women will die of the disease. Cervical cancer is more prevalent in less developed countries were accessed to screening is limited.

Many experts see the study results as a major break-through, though they acknowledge that published results are needed. In a formal statement, Debbie Saslow, Ph.D., director of breast and gynecological cancers for the American Cancer Society, called the vaccine an exciting advancement but noted that the data must be peer-reviewed and published.

If the vaccine is FDA-approved, it will likely need to be offered to both young women and young men. While men cannot get cervical cancer because they do not have cervixes, they can carry HPV and infect women through sexual intercourse.

Moreover, experts say that because there is no evidence that the vaccine will work on women that already have an HPV infection, guidelines for cervical cancer screening will still need to be followed even if the vaccine receives FDA approval. The American Cancer Society guidelines are as follows:

  • Cervical cancer screening should begin about three years after a woman begins having vaginal intercourse, but no later than 21 years of age.
  • Cervical screening should be done every year with regular Pap tests or every two years using liquid-based Pap tests. At or after age 30, women who have had three normal test results in a row may get screened every two to three years. A doctor may suggest getting the test more often if a woman has certain risk factors such as human immunodeficiency virus (HIV) infection or a weakened immune system.
  • Women 70 years of age and older who have had three or more normal Pap test results and no abnormal results in the last 10 years may choose to stop cervical cancer screening.
  • Screening after a total hysterectomy (with removal of the cervix) is not necessary unless the surgery was done as a treatment for cervical cancer or pre-cancer. Some other special conditions may require continued screening. Women who have had a hysterectomy without removal of the cervix should continue cervical cancer screening at least until age 70.

Source: American Cancer Society

Additional Resources and References

  • The October 6, 2005 Merck news release, "Merck's Investigational Vaccine GARDASILâ„¢ Prevented 100 Percent of Cervical Pre-cancers and Non-invasive Cervical Cancers Associated with HPV Types 16 and 18 in New Clinical Study," was published on the company's website,
  • The American Cancer Society provides cervical cancer screening guidelines on its website,
  • provides detailed information on cervical cancer screening, diagnosis, and treatment at