Cats typically spread URI viruses through sneezing and nasal discharge so if there is still discharge, your cat could still spread the virus. Many cats harbor Herpes virus for years and can start shedding again when stressed.
I would wait 3-4 weeks after the last vaccine booster is given. It is possible for the FIV+ cat to get symptoms of URI after vaccination. It depends on how well the immune system responds to the vaccine. Most likely, the vaccine will help limit symptoms though.
Vaccination of a particular cat is something that should be discussed and decided on between a cat owner and their veterinarian. It is my understanding that the URI (herpes and calicivirus) vaccine does not completely prevent the cat from getting the virus but it usually greatly reduces the severity of the symptoms. These two viruses are very contagious stable viruses that are very widespread among cat. Most cats are exposed when they are young and have developed some immunity to them. I believe keeping your cat vaccinated helps to keep their immune system primed to respond if they are exposed to the virus again. I recommend my patients get the vaccine every three years after they have had them two years in a row. I usually will vaccinate otherwise healthy FIV+ cats to help their immune system be prepared.
Vaccines can cause reactions but they are usually very mild. This is why a full exam by a veterinarian and discussion with the owner is vital. There are also different vaccines (at different prices) so discuss with your vet why they choose the vaccines they use.
I hope this helps. Write again if you have further questions.
Judy Karnia, DVM
Scottsdale Cat Clinic
Please also tell me if you think that a cat which has received a treatment for URI (but hasn't stopped wheezing) can remain contagious long after receiving the treatment.
If the answer is yes and I decide to vaccinate my FIV+ cat then how long should I wait after the vaccination before moving in with the wheezing cat ?
Is it still possible for my FIV+ cat to get a bad URI after being vaccinated ?
Thanks again for your help.