The approach described in the journal Science does not train the immune system.

[..] leaves white blood cells in our lungs [..] ready to jump into action no matter what infection tries to get in.

The effect lasted for around three months in animal experiments.

This stretches the definition of vaccine, and the effect is pretty short lived. What matter most I guess is that the spray works in clinical trials. It might be helfup to vulnerable people ahead of flu season.