Yes, it is necessary to cut both vas deferens to safely avoid pregnancy. If this were done unilaterally, the ejaculate would contain sperm from the non-vasectomized testicle.
Read the full article on: What is a vasectomy? The procedure its effectiveness explained ( 65).
Bachelor's Degree in Biotechnology from the Technical University of Valencia (UPV). Biotechnology Degree from the National University of Ireland en Galway (NUIG) and embryologist specializing in Assisted Reproduction, with a Master's Degree in Biotechnology of Human Reproduction from the University of Valencia (UV) and the Valencian Infertility Institute (IVI)