the effectiveness of the flu vaccine is dependent upon the extent of the match between the virus strains used to prepare the vaccine and those viruses in actual circulation. the age and health status of the individual also play a role in determining the effectiveness of the vaccine. research has shown that when there is a good match between the virus strains chosen for the vaccine and those in circulation the vaccine prevents influenza illness in approximately 70%-90% of healthy adults under 65 years of age. a study of children from one to 15 years of age showed that inactivated influenza vaccine was 77%-91% effective in preventing influenza respiratory illness. the effectiveness of the vaccine in preventing respiratory illness in people over 65 years of age is somewhat lower. among older people who reside in nursing homes influenza vaccine is most effective in preventing severe illness secondary complications and deaths. the vaccine can be 50%-60% effective in preventing influenza-related hospitalization or pneumonia and 80% effective in preventing influenza-related death although the effectiveness in preventing influenza respiratory illness can be as low as from 30%-40%.
how effective is the flu vaccine?