Normally, after a vasectomy, the ultimate goal is to achieve a zero sperm count, that is, azoospermia. However, in some cases, vasectomy fails and sperm production continues, though partially. In the months following a vasectomy, it is normal for sperm to continue appearing in post-vasectomy semen analyses, as they are able to survive for a few months in the seminal ducts until their complete disappearance.