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Cervical Cancer Vaccine May Lose Effectiveness During Ovulation

WASHINGTON, DC -- August 6, 2003 -- A new study has found that a vaccine against human papillomavirus 16 (HPV16), the virus that causes cervical cancer, produces antibodies against HPV16 at the site where cervical cancer develops--a promising indication of the vaccine's effectiveness. However, antibody levels appear to decrease around ovulation, raising the possibility that the vaccine may be less effective during that time. The findings appear in the August 6 issue of the Journal of the National Cancer Institute.

A vaccine is considered promising if it can produce an immune response (determined by levels of antibodies) at disease-specific sites such as the cervix. Past studies have shown that an HPV16 vaccine can trigger an immune response and protect against HPV16 infection. However, most of these studies involved women who were taking oral contraceptives (which regulate menstruation), and it is unclear what effect changes in hormone levels during the natural menstrual cycle would have on the vaccine's effectiveness.

To examine the influence of menstrual cycle stage and oral contraceptive use on antibody levels, Denise Nardelli-Haefliger, Ph.D., of the Centre Hospitalier Universitaire Vaudois in Lausanne, Switzerland, and Douglas R. Lowy, M.D., of the National Cancer Institute, and their colleagues administered the HPV 16 vaccine to seven women who were taking oral contraceptives and 11 women who were ovulating. The researchers collected blood and cervical secretions twice a week for 5 weeks and determined concentrations of anti-HPV16 antibodies during different phases of the menstrual cycle.

All of the women had relatively high levels of antibodies in their cervical secretions after immunization. Among women taking oral contraceptives, antibody levels remained relatively constant throughout the menstrual cycle. In contrast, levels of vaccine-specific and total antibodies in ovulating women were highest during the proliferative phase of the menstrual cycle and lowest around ovulation, suggesting that sex hormones may play a role in regulating antibody concentration at the cervix.

Given these findings, the authors say that it will be important to determine whether the vaccine will be as effective at protecting ovulating women from HPV16 infections as it appears to be for women taking oral contraceptives.

They suggest that the decrease in antibody levels during ovulation might be a mechanism to protect sperm from antibodies. It remains unclear whether such a decrease in antibodies translates into a decrease in vaccine effectiveness.


SOURCE: Journal of the National Cancer Institute

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