Both my boys have had it for a few years and have been fine. The first times when they were quite little, they y looked surprised when the spray went up their noses but then it's quickly on to big clap, high 5 and shall we stop at the playground on the way home.
All of mine have had the nasal flu spray. And they were all fine xx
My son had his few months back he got a runny nose from it but was all fine :)
Don't do it! Let him be