- The effects Prostvac, CV301 and MSB0011359C on the developing human fetus are unknown. For this reason, men must agree to use highly effective contraception (that is, methods with a failure rate of less than 1% per year) prior to study entry, for the duration of study therapy and at least four months after the last treatment administration. Should a woman become pregnant or suspect she is pregnant while her partner is participating in this study, she should inform her treating physician immediately.