CD4 and influenza: ,13 Recent studies employing ultrasound (US)-guided FNA to sample draining LNs (dLNs) have utilised FNA-derived dLN cell profiling to demonstrate the evolution of B and CD4+ Tfh cell responses to non-adjuvanted influenza and COVID-19 mRNA vaccination weeks and even months after immunisation.14, 15, 16, 17, 18