How effective is the influenza vaccine?
The effectiveness of influenza vaccination depends on the state of the person’s immune system, the age of the person being vaccinated, the degree of similarity between viruses in the vaccine and those circulating in the population, the (sub)type of the virus and the length of time from vaccination to exposure to influenza virus. These factors make it difficult to say exactly how effective the influenza vaccine is. Generally, vaccination prevents illness in about 70% of young adults and is less effective in the elderly.
