Fig. 4.

Schematic representation of vertical airflow in the restaurant R2 with outbreak of Omicron variant. Note. The upper partial layer which was polluted by the rising exhaled air stream assisted by rising plumes of body and even warm food. The cool clean air generated from the fan coil units with upper-room ultraviolet-C germicidal irradiation (UVGI), and also mainly from entrance. For the corner or the two VIP rooms (illustrated by the blue dotted line), if their temperature was lower than the main area, there would be a bi-directional flow with upper inflow and lower outflow. This would explain why the air polluted by the index case would “jump” to the “distant” corner or VIP rooms, and somehow bypass the tables in the main area.