The person stays immune from influenza for generally a year after getting influenza shots. However it depends on various factors also which may differ from person to person. It may also last less than a year. This is due to the fading effect of the vaccine and because of the ever changing influenza virus every year. So, one may have to repeat the shots every year due to the varying strains of the influenza virus. With the help of lot of research and advance technology the doctors have been successful in developing various influenza shots that stays effective for longer time duration.  

On the other hand, a small child is required to get two vaccination doses in the first year. Most of the people should get themselves vaccinated by influenza shots as soon as they come out in the market. They will come into effect completely only after two weeks. If you want to know more about influenza shots then you can also consult with your doctor or can even get information from the internet. Some people might need it every year while some may not depends on their physical conditions and their immune system. So make sure that get you vaccinated with influenza shots at regular intervals.