We had a meningitis scare with my wife's son Harry when he was about 15. He was fine when we went shopping at 7.00 pm just feeling a bit fluey, by 9.00 when we got home, he couldn't sit up on his own, was photo sensitive,running a huge temperature and was only semi -coherant and when we took him to the hospital they thought that was meningitis and moved like lightening as they said it can kill in as little as 3 or 4 hours.
As it goes it wasn't meningitis just a nasty virus, but they kept him in for five days until they were dead sure and took it super seriously, so yeah I believe it can be virtually non smptomatic until it's too late judging by the hospital's reaction.
My heart goes out to the young lad's family, no-one should have to bury their child.