Immunization of man and animals against influenza by oral and intranasal routes.

Live human and equine influenza virus strains modified by serial passage on allantois-on-shell system (AOS) in the presence of normal horse serum were administered orally or intranasally to volunteers or horses. Mostly mild clinical short-lasting reactions, replication in nasal mucosae, transmission to placebo recipients and significant local or circulating antibody rises were observed following administration to volunteers of strains modified by five or less serial passages on AOS in the presence of normal horse serum (NHS). Milder clinical reactions, no replication, no viral transmission and lower immunogenicity were observed when up to ten serial passages on AOS+ NHS were carried out. Similar results were observed in horses and colts. Heavy shedding of A/Eq-2 strain following the challenge was observed in placebo recipients. Colts immunized intranasally were completely protected while 33% of those immunized orally shedded small quantities of A/Eq-1 and A/Eq-2 viruses. However, a sharp rise of local antibodies against both strains was measured two days after the challenge in the three groups.