Cat Flu is horrible
Our vet gave Bob and the others AB jabs to help fight any resulting infection.
Congestion is the enemy you have to throw everything at. Bisolven is brilliant as long as he is eating altho, even if he stops, you can always rub it on his gums. I was going to mention the shower trick but see you have that covered.
Another trick I learned when Bobby had flu in July/Aug 2012 was to use Olbas oil. Obviously it must never touch the cat! I placed Bob in his carrier, closed door with a towel draped over it. I then put a few drops of Olbas oil in a bowl full of boiling water, put cling film over the top of bowl and made a few small holes in the cling film allowing steam to come out. I placed this outside the carrier at cage door end under the towel and left him for 20 mins. Also put drops of Olbas oil on a tissue in his room out of reach.
A little vaseline was applied to his nose when it got sore.
The small hours of the morning are generally worse I found and panic sets in when they stop eating. If he stops eating I would thoroughly recommend liquivite (get from vet) with a little boiling water added to warm it a little.
Have a look at this for more info and download the document.
Know your enemy http://www.bluecross.org.uk/1959-2765/cat-flu.htmlOur Bobby was fully vaccinated btw so don't beat yourself up on that score
Obviously need to get him sorted when he is over this. Sending every good wish.
Did the vet tell you about apple cider vinegar? I haven't heard of that.