To provide a delivery device and method for delivering substance, in particular a vaccine, to a mucosal surface within the oral cavity of a subject.

The delivery device includes a mouthpiece unit 10 and an oral outlet unit. The mouthpiece unit 10 is configured such that, on exhalation or attempted exhalation by the subject, a pressure is developed in the oral cavity to close the oropharyngeal velum of the subject. The oral outlet unit 14 includes at least one outlet 30, from which substance is delivered to a mucosal surface within the oral cavity of the subject, when it is used.