Injections of dead influenza virus may confer immunity to that particular strain of influenza. For this reason, vaccinations must be given each year as new strains develop. Vaccinations are usually given in the fall to confer maximum protection during the winter months. They are recommended for people over age 65 and those with chronic diseases. Experiments have been performed using a modified live virus, but these have not proved as effective as vaccinations with the dead virus.
Influenza is a contagious disease.
It is spread by inhaling infected droplets in the air, which are produced by coughing and sneezing. Influenza is most common during winter.