Five main studies involving around 18,000 children up to 6 years of age compared Fluenz with either placebo (a dummy treatment) or an injectable flu vaccine containing inactivated (killed) viral material from comparable flu strains. The flu strains were selected each year in accordance with the recommendation for the corresponding influenza season.

Four studies showed that, compared with placebo, two doses of Fluenz reduced the number of flu cases caused by the three strains in Fluenz by between 73% and 93%. Protection against flu caused by any strain (including strains not included in the vaccine) was between 70% and 86%.

In the main study comparing Fluenz with an injected flu vaccine containing comparable virus strains, Fluenz reduced the number of flu cases caused by the three flu strains in Fluenz by around 45% and against any strain by 55%. A supportive study showed that protection in children and adolescents aged 6 to 17 years was comparable between Fluenz and an injected flu vaccine.