i have a friend who has the same problem with his persian, he says persians are known for it, something i never knew, i have no answers really, but right now my cat is using flumax, which has the lysine in it, it's after her dental surgery as she is a flu carrier, even though vaccinated yearly, when stressed she can get a mild dose, i have to say so far so good, its been five days, there was a couple of sneezes but thats all and she seems to be responding, however it is expensive, cost me 42 dollars for a bottle ,although the bottle is large and lasts in to 2016, im in NZ ,but im sure there is an equivalent where you live, might be worth asking about.