Humans will naturally self isolate during real pandemics. As has been seen in the black death and many other plagues in history.

There is never a need for a government quarantine unless a known group is deliberately spreading a bio-weapon on a localized population. (i.e. like trolls in world of warcrafts corrupted plague who deliberately brought it to cities.) and even then it needs to actually be justified and not on an airborne flu.