Primary (0–28 day): frequency of vaccine events, frequency of serious vaccine events, proportion of subjects with positive T cell response
Secondary (0–28 day): mortality, duration of mechanical ventilation if applicable, proportion of patients in each category of the 7‐point scale (7, 14, and 28 days after randomization), proportion of patients with normalized inflammation factors (7 and 14 days after randomization), clinical improvement based on the 7‐point scale if applicable, lower Murray lung injury score if applicable (7 days after randomization)