Boulder Q: If a person gets the flu, do they become immune at all to the flu? Why is it necessary to continually get flu shots?
It wouldnt be if this werent among the most mercurial of viruses; it changes virtually from person to person by random mutation (drift) and it also can exchange huge hunks of DNA with another flu virus all at once (shift). So this years virus may be only slightly related to last years and you need a new shot.
