There are lot of studies done all together on CCR5 ..
I read interesting story recently , they think Delta32 mutation possibly happened first in Europe about 2500 years ago..

And when plaque happened in Europe in 6 century , and killed 30-50 mill people , about half of world population ,
most of the people with this mutation survived this plague ....

Now they calling plague , disease produced by Yersenia pestis , and they proved that CCR5 is not important for this disease , and Delta32 patients are not protected.

So theory is that what was called plague in the 6 century maybe really different infection then we see now , produce probably by some virus.

I thought it was interesting story....