[Comparative study of parenteral and oral immunization against influenza in a large clinical trial. 2. Results of immunologic studies].

In a multicentric trial 350 persons (19-24 years) were immunized with influenza vaccines containing the following virus antigens: A/Singapore/6/86, (H1N1); A/Mississippi/1/85, (H3N2); B/Ann Arbor/1/86. 174 received an i.m. injection of 0.5 ml "Influmun" vaccine from SSW Dresden/GDR. 176 persons were immunized twice within 60 days with enteric-wated capsules each containing approximately 60 micrograms hemagglutinin of all three virus strains. The volunteers were clinically observed in an interval of 6 months. The majority of orally immunized persons with low pre-immunization titers responded with fourfold or higher IgA antibody titer rises in nasal secretions, but no significant IgG antibody titer increase in sera could be observed. Secretory antibody titers remained elevated for 2 to 4 months. Parenterally immunized persons showed antibody titer rises in sera but not in nasal secretions. In both groups the highest antibody titer increases were observed after application of the A/Singapore/6/86 virus antigen. Volunteers with high pre-immunization titer did not show an antibody increase neither after parenteral nor oral immunization.