Catalysis of the reactions: (KDO)-lipid IVA + CMP-3-deoxy-D-manno-octulosonate = KDO2-lipid IVA + CMP, and lipid IVA + CMP-3-deoxy-D-manno-octulosonate = (KDO)-lipid IVA + CMP.
3-deoxy-D-manno-octulosonic-acid transferase activity