No – unfortunately, the level of protection provided by influenza vaccines varies and is not 100%. Influenza vaccines tend to work best in healthy adults and older children, though they are still effective in preventing hospitalisation of individuals who contract the disease despite having been vaccinated.
Furthermore, there are many different influenza viruses in circulation at once, not all of which will be included in the seasonal flu vaccine. The vaccine is designed to immunise against the viruses that research suggests will be most common.
Finally, vaccines do not work instantly, and so it is possible to catch the virus just before or soon after vaccination – in this case the vaccine may not prevent you from becoming ill.