August 8, 2003
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.
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).