However, some differences were observed: The vaccinated group had a higher frequency of specific CD4 \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${T}_{EM}$$\end{document}TEM cells compared to recovered COVID-19 patients (Dennehy et al. 2021). Here, CD4 is linked to COVID-19.