No, antibiotics will not help genuine cat flu because this infectious disease is caused by a virus and antibiotics are prescribed to cure bacterial infections not viral infections. However, often a viral infection can lead to a secondary bacterial infection which is why veterinarians sometimes prescribe antibiotics if they see a patient with cat flu. They are playing safe and sometimes they might be overprescribing antibiotics. I discussed this issue on another page which you can read by clicking on this link.
It is believed that two major viral groups are responsible for the majority of upper respiratory infections in cats and these are the herpesvirus group and the calicivirus group. There are other viral agents including the reovirus group but they account for a minority of cases.
Antibiotics kill bacteria and they target (1) the cell wall or membranes that surround the bacterial cell and/or (2) the process that makes the nucleic acid DNA and RNA and/or (3) the processes that produce proteins. And so, they disrupt essential processes or structures in the bacterial cell which kills bacteria or slows down bacterial growth. But they are ineffective against viruses.
Viruses are very tiny infectious agents which contain genetic material, either DNA or RNA. They have a core of DNA or RNA which is surrounded by a protective coat called a capsid which is made up of protein. They must invade a host in order to multiply.
The fact of the matter is that with respect to feral cats, especially kittens, you see upper respiratory infections almost invariably leading to secondary bacterial infections of the eye which is conjunctivitis which at the end of the day often destroys the eyeball. They go blind. That’s what happens when you let a bacterial infection in a cat progress untreated to the endgame.
Respiratory viral infections facilitate secondary bacterial infection because they negatively impact the cat’s immune system through the overproduction of inflammatory cytokines. Cytokines are small proteins crucial in controlling the growth in activity of immune system cells and blood cells. They signal the cat’s immune system to do its job.