Zeferino, a three-time Olympian, first competed for Cape Verde in a meet in Maia, Portugal setting a national record in the 3000 metres steeplechase which still stands today. The following year at the 1996 Summer Olympics in Atlanta, Zeferino made history along with Henry Andrade and Isménia do Frederico by becoming the first athletes to represent the tiny African nation at the Olympic Games. In the men's marathon he finished 94th in a time of 2:34:13. The following year he competed in the 1997 World Championships, finishing 37th in the marathon with a time of 2:25:56. Two years later in February 1999, Zeferino recorded his best ever time in the marathon at the Sevilla Marathon finishing in 2:23:16. Six months later at the 1999 Championships, he finished the marathon slightly slower in 2:26:03 which placed him in 39th position. At the 2000 Summer Olympics in Sydney, Zeferino improved on time and position from four years earlier crossing the line in 67th place in a time of 2:29:46. The following year, he completed at the 2001 World Championships, where he finished the marathon in 51st place in 2:32:46. Zeferino's final race was the marathon at the 2004 Athens Games where aged 38, he finished in 78th with a time of 2:36:22.