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In: Vaccines for fertility regulation: the assessment of their safety and efficacy. Proceedings of a Symposium on Assessing the Safety and Efficacy of Vaccines to Regulate Fertility, convened by the WHO Special Programme of Research, Development and Research Training in Human Reproduction, Geneva, June 1989, edited by G.L. Ada, P.D. Griffin. Cambridge, England, Cambridge University Press, 1991. 247-50. (Scientific Basis of Fertility Regulation)The 3 human chorionic gonadotropin (hCG) vaccines have shown the most potential for stimulating antibody production, but clinical trials have not yet tested for fertility reduction. Antifertility vaccine research began 20 years ago and it has taken this long to et this far because investigators have had to deal with the interaction of 2 complex systems--the immune system and the endocrine system. An example of this complexity is that no one understands why exogenous whole hCG does not induce a booster effect in hCG immunized women. Antifertility vaccines require much more effort than conventional antidisease vaccines because they will probably be used more often and more extensively than other vaccines. WHO should coordinate the trials of the 3 different vaccines to assure that researchers can designate the optimum preparation for particular cases. Other research indicates that cells and cell products may be vaccine candidates. Researchers may even try immunizing against other hormones beside hCG, gametes or their products, or the trophoblast. They may soon develop a T-cell vaccine which would be against the trophoblast. They speculate that eventually a composite vaccine will emerge which would have several targets therefore providing effective contraception and minimizing the immunological activity needed from each individual component. Biotechnology has allowed researchers to screen for many proteins such as those on the surface of spermatozoa which it can produce in great numbers. It may even be able to also screen for and manufacture carbohydrates making the zona pellucida to be a vaccine target. Potential areas of conflict once a vaccine is available are issues of ethics, national priorities, foreseeable abuse, and balance between individual rights and needs of future generations. Already contrasting points of view exist about an antifertility vaccine. Nevertheless the gravity of the demographic crisis calls for effective family planning technologies.