Figure 1. Vaccine-binding and H5 pseudotype-neutralizing antibodies in plasma samples collected before and after seasonal influenza vaccination.

Volunteers (A to X) were immunized with seasonal influenza vaccine in 2 consecutive seasons. Plasma and PBMC samples were collected before and 2 weeks after vaccination. (A and B) Vaccine-specific IgG was measured in plasma by ELISA using the homologous vaccine as antigen. Reciprocal EC₅₀ values before (white bars) and after vaccination (black bars) in 2007 (A) and 2008 seasons (B) are shown. (C and D) H5-specific neutralizing titers were measured in the same plasma samples by a pseudotyped neutralization assay against an H5 pseudovirus (A/VN/1194/04). Reciprocal ID₅₀ values before (white bars) and after vaccination (black bars) in 2007 (C) and 2008 (D) are shown. (E and F) Correlation between the increase of vaccine binding titers (E) and H5-neutralizing titers (F) following vaccination in 2007 (x axis) and 2008 (y axis) in the 9 donors that received the seasonal influenza vaccine for the 2 consecutive years.