Having to provide repeated semen samples following a vasectomy could soon be a thing of the past, after 96 percent of men were given the all-clear based on a single test three months after surgery. Fifty-one percent of the 1,073 samples contained no sperm and a further 45 percent contained less than 100,000 immotile sperm. No paternity was reported in the cleared group after a follow-up of at least a year.