Intuitively at least, there is. If 90% of the herd is immune, really immune, then a pandemic has a limited number of hosts, so can't rage at the same rate that it could against a herd that is 5% or 20% immune.
100% immunity isn't required in order to prevent pandemic.
i don't see herd immunity as having any play in the WuFlu event, at least not yet.
Functionally, herd immunity works like picking individuals out of the transmission path here and there. As a result various strands die off as they are not replicated, which in turn causes it to act as a much less virulent disease.
It is being overused in the discussions of how to deal with this coronavirus outbreak, but as you note, it is certainly a thing.