Prevention of feline upper respiratory disease, commonly known as 'cat flu' is traditionally achieved by two types of vaccination: live vaccines administered by intranasal or by parenteral inoculation or parenteral inactivated vaccines with an adjuvant. Both of these have been associated with side effects. The objective of the development of a new generation of cat flu vaccines was to market a vaccine which was perfectly safe in all epidemiological situations and was as potent as the current products available on the market.