IN PREVIOUSLY IMMUNIZED ELDERLY ADULTS INACTIVATED INFLUENZA-A (H1N1) VIRUS-VACCINES INDUCE POOR ANTIBODY-RESPONSES THAT ARE NOT ENHANCED BY LIPOSOME ADJUVANT

In a randomized double-blinded study, 77 healthy elderly seropositive volunteers (95% of whom had received influenza vaccine within the prior 5 years) were immunized with either monovalent liposome-adjuvanted or control Subvirion vaccine containing inactivated influenza A/Taiwan/1/86 (HIN1) virus. The experimental vaccine was well-tolerated but elicited serologic responses that were no different in frequency or magnitude from those induced by the control vaccine. Less than 20% of subjects in either group mounted a fourfold or greater rise in antibody titer. Sixty-three elderly subjects who had participated in the liposome vaccine trial were reimmunized 18 weeks later with licensed trivalent subvirion vaccine and their serologic responses were compared with those of 26 young adults, Significant rises in hemagglutination inhibition (HAI) antibody titers to the A/Texas/36/91 (HIN1), A/Beijing/32/92 (H3N2) and B/Panama/45/90 components occurred in 10%, 76% and 56% of elderly vaccinees, respectively, compared to 92% (p < 0.0001), 100% (p < 0.005) and 88% (p < 0.005) of young vaccinees, respectively. Age differences in seroresponse rates to the HIN1 subtype antigen were significant even when comparing young and old adults with identical prevaccination HAI antibody titers. These data confirm prior observations suggesting that previously immunized elderly persons have impaired serologic responses to influenza vaccines, particularly against recently circulating HIN1 subtype antigens. It remains un clear whether liposome-adjuvanated formulating would have an advantage over conventional influenza vaccines for routine annual reimmunization of targeted populations.