PSMD1 and susceptibility to pneumonia measurement: The results of Spearman’s correlation analysis demonstrated a statistically significant positive relationship between neutralizing antibody titers and anti-S1 IgG, anti-RBD total Ig, and anti-S1 IgA levels; in the ‘without pneumonia’ group: rs = 0.73, p-value < 0.001; rs = 0.67, p-value < 0.001; rs = 0.59, p-value < 0.001, respectively, and in the ‘with pneumonia’ group: rs = 0.62, p-value < 0.001; rs = 0.53, p-value < 0.001; rs = 0.50, p-value < 0.001, respectively (S1 Fig).