Not for some weeks
from going into semen
, and should include: the surgery, using other birth control
to collect the next 20 ejaculations (for 6 weeks), and then giving a semen sample at the urologist's office to be sure no more sperm is in the semen.
After all three of these things are done, a vasectomy is effective (extremely low failure rate of approx.1 in several thousand men).