In order to understand this article you will need to use your powers of visualization. I want to try and explain why the usual flu vaccine is not 100% effective and how researchers are trying to develop a vaccine which will be totally effective.
Visualize a round ball with spikes or stalks sticking out from all around the surface. There is a coating on these stalks and the composition of the coating determines the strain of influenza virus. The usual flu vaccine is directed against the covering on the stalks. The composition of this covering changes and the changes can give the virus immunity from the current vaccine. This is a simple explanation of a much more complex issue, but it serves the purpose.
To get a vaccine that can protect against any influenza virus, regardless of the covering on the stalk, the vaccine must attack the stalk which appears to be the same no matter what the covering. Researchers believe that a vaccine against the stalk of the influenza virus will provide universal immunity no matter what strain of influenza is produced each year.
The development of influenza vaccines was hampered in the past by the need to culture the virus in eggs. It also meant that anyone allergic to eggs should not be given the vaccine. Today, it is possible for vaccines to be produced in dog kidney cells, which do not have the limitations of egg-based vaccines. The effectiveness of these cell-based vaccines is under study.