A developmental process, independent of morphogenetic (shape) change, that is required for the vagus nerve to attain its fully functional state. This nerve is primarily sensory but also has visceromotor components. It originates in the brain stem and controls many autonomic functions of the heart, lungs, stomach, pharynx, larynx, trachea, esophagus and other gastrointestinal tract components. It controls some motor functions such as speech. The sensory branches mediate sensation from the pharynx, larynx, thorax and abdomen; it also innervates taste buds in the epiglottis. [ GOC:cls http://purl.obolibrary.org/obo/go/references/0000021 GOC:dgh GOC:dph https://www.worldcat.org/search?q=bn%3A0838580343 GOC:jid ]