[header] How to prevent feline upper respiratory illness [title] Get your cat vaccinated. [step] Vaccination against cat flu is considered an essential vaccine. The flu vaccine needs to be given regularly and it comes in a variety of types (modified live, modified live intranasal, killed vaccine) which determines how often the vaccine needs to be given. 
[substeps] A typical vaccine regime is an initial loading dose of two injections given 3-4 weeks apart followed by a booster one year later, then further booster injections every three years. This is just a guide and varies depending on which vaccine is used.