CD4 and influenza: Using pMHCII-tetramer technology, we analyzed HA118-132- and HA306-318-specific CD4 T cells ex vivo in HLA-DRB1*01:01-positive individuals who received influenza vaccination in 2016/2017, 2018/2019, 2019/2020, and/or 2020/2021 (see also Table 2 and Supplementary Table 1).