Fig. 1From: Investigation of CD4 and CD8 T cell-mediated protection against influenza A virus in a cohort studyTimelines of our study and local influenza activity for pH1N1 (red) and H3N2 (blue) virus from 2009 to 2013. Shaded regions represented the period for the 10 rounds of serum collections (R1 to R10) and 4 rounds of whole blood collections (R1, R3, R5, and R7). The gray period indicated the rounds with CD4 and CD8 measurements. Arrows indicated the pre-existing CD4 and CD8 response and the corresponding epidemicBack to article page