Detroit ? The seasonal flu shot is more effective at preventing flu than the nasal spray in healthy adults, which may disappoint those afraid of needles.

University of Michigan researchers said of 2,000 young adults studied, only a handful were confirmed with flu, which means overall, the vaccines are effective. However, of those who got sick but had had a vaccination, most had gotten the nasal spray instead of the shot.

The vaccines are prepared differently, said study leader Dr. Arnold S. Monto of the U-M School of Public Health’s Department of Epidemiology. This may explain why one works better than the other. The shot is made of dead viruses, and the nasal spray of live, but weak, viruses.

“People don’t think of the fact that the live-virus vaccine works by infecting people,” Monto said of the nasal spray. Children, especially those younger than 6, are a little different, Monto said, because they don’t have the seasonal flu exposure of older children and adults.