Gary - post this in Cat Health and you will attract a few more responses, I think. I know that this is part of the standard cat vaccinations where I live, part of the "combo" shot.

What did your vet tell you about it?

I know it is also called "Cat Flu". Here is a link and some quotes from it:

http://www.cat-world.com.au/FelineCalicivirus.htm

In the healthy adult cat, the mortality rate is fairly low, however kittens & older cats are at greater risk. Feline calicivirus is most often seen in shelters & environments with over crowding, although it can occur in any household.
How is it treated?

Treatment is generally supportive. As calicivirus is a virus, antibiotics won't work, however they may be prescribed for secondary bacterial infections.

Removal of discharge from the nose & eyes will make your cat more comfortable.

If the cat has become anorexic, force feeding may be necessary. Fluids may also be required to treat dehydration.

Prevention of feline calicivirus:

Routine vaccination.

Avoiding overcrowding of feline populations, reducing stress.
http://www.cat-world.com.au/CatFlu.htm

How is cat flu treated?

Treatment depends on the cause of the cat flu. There are no drugs to treat viral infections & supportive care is necessary. This includes keeping the nose clear of discharge. A stuffed up cat will often lose it's appetite, therefore it is of utmost importance that you do everything you can to encourage your cat to eat & drink. If your cat refuses to eat/drink then please seek veterinary advice immediately.

Even if the cause is viral, antibiotics may be prescribed to protect against secondary bacterial infections.