Fig. 2.

Effect of preexisting T cell responses to seasonal H1N1 virus on the Ab responses to the 2009 H1N1 vaccine. (A and B) Proportions of subjects with seroconversion or a ≥4-fold increase in Ab titer to 2009 H1N1 (A) and a fold increase in Ab titer to 2009 H1N1 (B) were compared between groups with or without preexisting T cell responses to seasonal H1N1 particles, as measured by IFN-γ ELISpot assay. Error bars represent 95% confidence intervals. A P value of <0.05 was considered statistically significant. ns, not significant.