(3) The % C5aR1-expressing neutrophils of pneumonia (non-COVID-19) patients increased slightly but significantly (p < 0.0001), with a large effect size (d = 9.78), but those of ARDS (COVID-19) patients increased ten times more than those of pneumonia (non-COVID-19) patients significantly (p < 0.0001), with a large effect size (d = 8.90), for the passage of time mentioned above. Here, C5AR1 is linked to acute respiratory distress syndrome.