Local and systemic immune response in nursing-home elderly following intranasal or intramuscular immunization with inactivated influenza vaccine

Intramuscular (IM) influenza vaccines are only 30-40% effective in preventing clinical illness among the elderly, and their effectiveness in eliciting mucosal response may be even lower. The aim of the present study was to evaluate the immunological effect of a novel inactivated intranasal (IN) trivalent whole influenza virus vaccine among nursing-home elderly. Twenty-one institutionalized elderly subjects were vaccinated IN with an inactivated novel vaccine, twice, 21 days apart, and with no adverse effects. Twenty-two subjects were vaccinated once with a commercial IM vaccine. Viral strains used in the 1998/9 vaccine (20μg of each per dose) were A/Beijing/262/95, A/Sydney/5/97 and B/Harbin/7/94. Serum antibodies (IgG and IgM) and nasal IgA were determined by the hemagglutination inhibition (HI) test and enzyme-linked immunosorbent assay (ELISA), respectively. Mucosal antibody response to the three vaccine strains was detected in 47.6-71.4% and 18.1-31.8% of IN and IM immunized subjects, respectively. Serum antibody response to the three antigens tested was detected in 20.0-61.9% and 18.2-72.7% of IN and IM immunized subjects, respectively. Seroconversion was not significantly different after IN or IM vaccination for both A/Sydney and B/Harbin, but higher for A/Beijing following IM vaccination. On study completion, 57.1, 65.0 and 50.0% of IN vaccinees were seroprotected to A/Beijing, A/Sydney and B/Harbin, respectively. Similarly, 68.1, 77.2 and 54.5% were immune after IM vaccination. The IN vaccine tested was significantly more effective than the IM vaccine in inducing mucosal IgA response. This may prevent influenza at its early stages and thus contribute to the reduction of morbidity and complications in nursing-home elderly.