- The effects of PROSTVAC in combination nivolumab, ipilimumab or both on the developing human fetus are unknown. For this reason men must agree to use adequate contraception (abstinence, vasectomy) or female partner must use (intrauterine device (IUD), hormonal [birth control, pills, injections, or implants], tubal ligation] prior to study entry and for up to 5 months after the last dose.