C5AR1 and susceptibility to pneumonia measurement: (5) The % C5aR1-expressing monocytes of pneumonia (non-COVID-19) patients increased significantly (p = 0.0002), with a large effect size (d = 1.29), but those of ARDS (COVID-19) patients increased two-and-a-half times more than those of pneumonia (non-COVID-19) patients significantly (p < 0.0001), with a large effect size (d = 3.13), at the passage of time mentioned above.