At least three polio vaccinators were killed following an improvised explosive device (IED) explosion in southern Helmand province of Afghanistan on Tuesday.According to local government officials, the incident took place Tuesday at midday near Sangin district after their vehicle struck with the improvised explosive device (IED), Pajwok afghan news agency reported.Provincial governor spokesman, Omar Zwak, said the vaccinators were their way to give polio drops to children when the incident took place. No group including the Taliban militants has so far claimed responsibility behind the incident.