- Pregnant or lactating women. Women of child bearing potential must be using effective contraception for at least 30 days prior to initial immunization, unless for religious, social, or medical reasons they do not intend to have children and are practicing sexual abstinence. Subjects using birth control must agree to do so for the entire 64 week study period. Acceptable method of birth control is defined as hormonal contraceptives, intrauterine device (IUD), diaphragm with spermicide, condoms, a vasectomized partner or abstinence.