Comparison of long-term systemic and secretory antibody responses in children given live, attenuated, or inactivated influenza A vaccine.

A comparison of inactivated intramuscular and live intranasal influenza A vaccines in young children undergoing primary immunization might be expected to show differences in serum and local mucosal antibody responses. To demonstrate such differences, serum and local respiratory tract antibody responses of young children vaccinated with intranasal live, attenuated, cold-adapted (H3N2 or H1N1), or intramuscular inactivated (H3N2) influenza A vaccines were examined for one year after vaccination. Antibody responses were measured by hemagglutination-inhibition (HAI) and class-specific enzyme-linked immunosorbent assay (ELISA). One year after vaccination, live intranasal vaccinees had significantly less decay of serum HAI (p = 0.025) and IgG antibody (p = 0.01) directed against the influenza hemagglutinin and neuraminidase than did intramuscular inactivated vaccinees. Nasal secretory IgA developed almost exclusively in live vaccinees and persisted for up to one year. Persistent nasal secretory IgG was detected in both live and inactivated vaccinees. Live vaccination not only stimulates a more durable serum antibody response, but also induces long-lasting local respiratory tract IgA antibody that may play an important role in host protection.