My brother bought a Maine Coon Kitten about 3 years ago and poor Chester is a carrier of calici virus but has also had many other problems with his digestive system and has had to have all hi teeth out.
He has not grown to his full size and compared to healthy Maine Coons looks very thin and sickly. He was also not socialised properluy and is scared of most things.
I now the breeder was not a member of the Maine Coon Breeders Club as she refused to be one..........always sounds suspicious to me!
Chester was a gorgeous kitten until all the problems started although he was already scared of things.
I would definately get back on to the breeder becuase insurance could be an issue unless he already has insurance, and I know that it has cost £1000s to get Chester to the stage he is at but he will continue to have problems all of his life.
As Tersa says you would have to stay with the insurance provided, which is likely to be with pet plan I think.
If this is a reputable breeder then things should be able to be sorted out.
I really hope that this is just a sniffle that is not anythiung bad