Is pregnancy possibly after a vasectomy?

Certainly!! The only sure way is abstinence. Most common reason for early vasectomy failure is having unprotected intercourse too soon without checking the Post vasectomy semen analysis. There are plenty of residual viable sperms after the vas deferens are cut. It can take more than 20 ejaculations after to clear them. That's why it's important to use back up contraception until proven otherwise. Of course, there is other rare cause like recanalization of the vas deferens. Some reports that different vasectomy techniques may have slight higher incidence of this. Unfortunately, none is 100% sure. I have met couples who both had sterilization procedures because of their fear of the failure rate.