a flu shot will be effective if is well matched, meaning the immunization matches that year's influenza viruses. if a flu shot is well matched, it will give the body a flu shot will be effective if is well matched, meaning the immunization matches that year's influenza viruses. if a flu shot is well matched, it will give the body additional helper t cells within the organs of the body the ability to use a pathogen to stimulate antigens the ability to remember an encounter with a specific organism the ability to tell a harmful pathogen from a harmless one