Birth-control vaccine safe in early tests.

Birth-control vaccine safe in early tests

Clinical trials of an experimental birth-control vaccine reveal no major side effects, say researchers at the Flinders Medical Center in Adelaide, Australia. Injections of the vaccine, which triggers production of antibodies to neutralize a hormone necessary for pregnancy, left a few women with localized muscle pain but caused no general side effects.

Tests of the vaccine's ability to prevent pregnancy will come later. Ideally, one dose would last six months to a year, during which time antibodies would bind to human chorionic gonadotropin (hCG), making it impossible for a fertilized egg to implant in the uterine lining. To induce this immune response against a woman's own hormone, scientists developing the vaccine anchored a synthetically produced portion of the hCG molecule to diphtheria toxin, a combination capable of inducing strong antibody reaction against both substances. Since the antibodies target a hormone released by a fertilized egg, vaccinated women should have normal levels of other hormones and uninterrupted menstrual cycles, say the researchers in the June 11 LANCET.

Several weeks after the group injected varying doses of the vaccine into 30 surgically sterilized women, they found hCG antibodies in all 30. The question remains: How strong does the antibody reaction have to be to block pregnancy? Although primate tests have given a general idea, no one can be sure until the second phase of human trials, says the vaccine's developer, Vernon Stevens of Ohio State University in Columbus, who participated in the Australian study.

"The baboon studies are not exactly identical [to human studies]," Stevens says, adding that they have shown the vaccine to prevent pregnancy in animals.

Experimenting with a birth-control vaccine that uses the tetanus rather than diphtheria toxin to stimulate antibodies is G.P. Talwar of the All India Institute of Medical Sciences in New Delhi (SN: 6/7/86, p.365). Along with scientists at the New York-based Population Council, Talwar tested his version of the vaccine on 15 women in 1980, finding a weaker-than-expected antibody response to hCG.

One problem with previously tested hCG vaccines, Stevens says, was that women also formed antibodies against luteinizing hormone (LH), similar in shape to hCG. Inactive LH means disrupted menstrual cycles, and even early menopause in some cases. Since Stevens' vaccine uses a protein segment unique to hCG, women in the Australian study did not produce LH antibodies.

Stevens hopes to have U.S. efficacy tests underway next year.