Serum antibody off-rates to H5-Viet-rHA1 (but not rHA2) following heterologous prime-boost strongly correlate with the in-vitro neutralizing capacity against the homologous H5 vaccine viruses.

Antibody off-rate constants were determined directly from the serum sample interaction with H5N1 rHA1 or rHA2 proteins using SPR in the dissociation phase. SPR analysis of post-boost vaccination human sera from all 3 vaccine groups combined was performed with rHA1 (A) or rHA2 (B) of the H5N1-A/Vietnam/1203/2004 strain, or rHA1 of the heterologous H5N1-A/Indonesia/5/2005 (Clade 2.1) strain (C). Each symbol represents one individual. Serum samples on day 28 following single H5N1 booster vaccination with the subunit H5N1 vaccine (Sanofi Pasteur, 90 μg HA/dose) from the low-dose Ad4-H5-Vtn adjuvanted primed (red circles), high-dose Ad4-H5-Vtn primes (blue circles), or unprimed (green circles) are shown. Antibody affinity of post-H5N1 vaccinated human sera against HA1 (but not HA2) of H5N1-A/Vietnam/1203/2004 correlated with the homologous virus microneutralization titers (MN) against the A/Vietnam/1203/2004 (H5N1). Similarly, polyclonal antibody affinity of post-H5N1 vaccinated human sera against HA1 of the heterologous H5N1-A/Indonesia/5/2005 (Clade 2.1) strain correlated with the microneutralization titers (MN) against the A/Indonesia/5/2005 (H5N1) virus. Spearman correlations are reported for the calculation of correlations between off-rate and MN titers combined across all vaccine groups.