* Deir al-Zor left out on grounds most residents had left
* But province has had a large population throughout the war
* Deir al-Zor vaccinated in Jan 2013 but coverage still too low
* Not clear why it was singled out
By Oliver Holmes
BEIRUT, Dec 17 (Reuters) - The Syrian government excluded the largely rebel-held province of Deir al-Zor - where polio broke out this year - from a...