Cross-reactive anti-hemagglutinin (HA) IgG responses are shaped by previous long-interval monovalent H5 vaccination and highly correlated with HA antigenic distance

Avian H5 influenza is an emerging influenza strain with the potential for human pandemic spread. One unresolved issue in pandemic vaccine preparedness is to what extent a vaccine recall response depends on the interval between the priming and boosting vaccinations. In this study, we analyzed the anti-H5 HA IgG responses to an H5 A/Indonesia/5/2005 boosting vaccination in three cohorts: (1) a short interval boosting cohort that received a prime and boost 28 days apart, (2) a long-interval boosting cohort that received an H5 A/Vietnam/203/2004 priming vaccination 5 years before boosting, and (3) a double long-boost cohort that received single doses of all three vaccines separated by 5-6 year intervals. Anti-HA IgG levels were measured using a multiple-plex assay against 21 H5 and 16 seasonal strains covering both influenza phylogenetic groups. We used the antigentic distance between the vaccine strain and each HA in the assay panel to de1ne the antibody response landscape. Both single and double long-interval boosting with the H5 variant vaccine elicited a broad antibody response to all H5 subtype strains, and double boosting resulted in sustained, vaccine-speci1c, anti-HA IgG levels over a six month period. Antibody-mediated immune responses were shaped by prior H5 exposure history, and the magnitude of both vaccine speci1c and cross-reactive anti-H5 HA IgG responses was highly correlated with the relative antigenic distance between the measured and the vaccine HAs. We conclude that the relative antibody landscape method can be used to quantify the phenomenon of antigenic imprinting on human influenza vaccine immune responses. IMPORTANCEA signi1cant obstacle to development of a universal influenza vaccine is understanding the relationship between multidimensional host humoral immunity, prior antigen exposure, and viral antigenicity. In this study, we used a multiplexed antibody assay to measure antibody cross-reactivities against antigenically similar H5 influenza virus strains. This work uses a novel method, relative antibody landscapes, to analyze the relationship between immune response and antigenic distance between the target H5 vaccine HA and other HAs in the assay after a boosting vaccination. This method improves analysis of immune responses by relating antigen exposure history to the influenza vaccination antibody response. This study also revealed that multiple vaccine boosting over several years can generate high levels of long-lasting cross-reactive antibodies against the priming H5 strains vaccine that subjects received, suggesting the HA imprinting mechanism(s) have a strong influence in the adult antibody response to H5 MIV vaccination.