How can you explain to someone that they need a flu vaccine every year and who should receive them?
(i.e., compare "drift" vs "shift")
drift: (changes over time) infected person develops Ab against that virus. As antigenic changes accumulate, the Ab created against the older viruses no longer recognize the “newer” virus, and the person can get sick again (drift; flu B, C).
shift: a sudden, MAJOR change in Influenza A only since it infects more than just humans (e.g., H1V1 pandemic of 2009).
>6 months old and >65 yo should be vaccinated.