In animals,viral infections sometimes remain localized. This means that they are limited to one area. This is the case for respiratory viruses such as influenza. the 'fiu' is an infection of the repiratory passages that is spread by breathing in airborne cells infected with influenza viruses. Vaccines can help reduce the number of cases of influenza. However,there are so many strains of the virus that it is impossible to provide immunity from all of them.