The influence of sequential annual vaccination and of DHEA administration on the efficacy of the immune response to influenza vaccine in the elderly

The present study examined the effect of repeated vaccination and of dehydroepiandrosterone (DHEA) treatment on the immune response to influenza vaccine in elderly subjects. Seventy-one elderly volunteers, aged 61-89 years, enrolled in a prospective randomized, double-blind study to receive either DHEA (50 mg qd p.o. for 4 consecutive days starting 2 days before immunization) or placebo. Antibody response against the three strains of vaccine was measured before and 28 days after vaccination, and compared between previously vaccinated and non-vaccinated subjects. DHEA treatment did not enhance established immunity. A significant decrease in attainment of protective antibody titer (titer of 1:40 or greater) against A/Texas in subjects with non-protective baseline antibody titer was recorded following DHEA treatment compared to placebo (52 vs. 84%, P < 0.05). Post-immunization titers against influenza A strains were significantly higher in those subjects who were never immunized before. Additionally, post-vaccination protective titers against the A/Johannesburg strain were more prevalent in those subjects who were never vaccinated before. The results were not the same for anti-B/Harbin antibodies - repeated vaccination caused a non-significant increase in HI titer in previously vaccinated subjects.