CD4 and infection: We measured SARS‐CoV‐2‐specific antibodies (including neutralizing antibodies), SARS‐CoV‐2‐specific CD4+ T cells, and SARS‐CoV‐2‐specific CD8+ T cells in all individuals in the cohort, with an emphasis on acute cases in elderly patients across two categories of COVID‐19 severity in Changhai Hospital, Shanghai, during the Omicron infections that appeared nationwide in China from December 2022 to February 2023.