there are around 13 different flu viruses roaming around at any given time. the flu shot only is for the expected top 3. i haven't had the flu shot in over 17yrs and have never gotten sick since i quit them. even when working in the hospitals. and i the last few years ive spent a lot of time at hospitals due to my injuries. the only time i can recall ever actually getting sick were back when i was always getting vaccinated.