Collectively, for the first time, our study provides evidence that delayed antibody responses correlate with poor clinical outcome of COVID‐19 patients. This notion is strongly supported by the reduction of SARS‐CoV‐2‐specific IgM and IgG levels and frequencies of ASCs and TFH cells in the early stage of disease in deceased patients compared with survived patients, which highlights the importance of early adaptive immune responses in patients with COVID‐19.