Because the mucosa-associated lymphoid tissue
(MALT) mucous-membrane immune system constitutes one
network covering the whole body, and because lymphocytes
are able to migrate, oral immunization also provides systemic
immunity expressed by the mucous membranes of other organs.
LAB strains, acting as carriers of S. pneumoniae antigens,
have already been shown to be effective at intranasal
immunization (see below)