Study: Cervical Cancer Vaccine May Wane During Ovulation

New research suggests an experimental vaccine against cervical cancer might lose some effectiveness when a woman ovulates. Certain strains of the human papillomavirus cause most cervical cancer, and scientists are trying to develop a vaccine to fend off the riskiest strains of the virus.

An early-phase trial of Merck & Co.'s vaccine generated excitement last fall when it appeared highly effective for at least a year after inoculation. But most of the women in the trial were also taking oral contraceptives, according to Dr. Douglas Lowy of the National Cancer Institute.

Because hormonal changes during the menstrual cycle can alter levels of virus-fighting immune cells in cervical tissue, Lowy and a Swiss colleague, Denise Nardelli-Haefliger, conducted a study to see if that were true for the HPV vaccine as well.

They gave the vaccine to seven women who took birth control pills and 11 women who did not. In the non-pill users, levels of HPV-fighting antibodies fluctuated substantially, reaching their lowest point around ovulation, the scientists reported. Women taking the pills had consistent antibody levels throughout the month.

Lowy said the study did not measure whether the vaccine is less protective in women who ovulate. He called for the advanced studies of the HPV vaccine that are currently underway to directly examine whether the drug prevents viral infection as well in ovulating women as in those who do not ovulate. Merck officials did not return phone calls asking if they plan to study the issue.

The report, "Specific Antibody Levels at the Cervix During the Menstrual Cycle of Women Vaccinated with Human Papillomavirus 16 Virus-Like Particles," was published in the Journal of the National Cancer Institute (2003;95;(15):1128-1137).

Back to other news for August 8, 2003

Search the Newsroom archive