The purpose of the study was to determine which factors correlate directly with response to vaccination in such a group of subjects with non-protective HI antibody titers before vaccination. Two vaccines were used, a subunit virus vaccine adjuvanted with MF59 and a split virus vaccine. The analysis indicated that immunization with vaccine adjuvanted with MF59 was an independent variable for immune response against A/H3N2 (OR: 3.51; 95% CI: 1.81-6.79) and B (OR: 2.31; 95% CI: 1.37-3.89). The results suggest that antibody response to vaccine is satisfactory in elderly people previously lacking a protective antibody titer, and that the adjuvanted vaccine reveals a better immunogenicity.