The Wells-Riley calculation for the ancestral strain of the virus produced suggested that for an individual to have under one percent chance of being infected, the room or building had to enjoy a ventilation rate of 100–350 cubic meters per hour if the individual was in there for 15 minutes, and 1200–4000 cubic meters per hour if in there for three hours.
 
The researchers found that for all three variants of concern, ventilation rates had to increase substantially to ensure an infection probability of under one percent.
 
For alpha, this meant ventilation rates of 650–1,200 cubic meters per hour for 15 minutes of exposure, and 8,000–14,000 cubic meters per hour for three hours of exposure.
 
For delta, the rate jumped up further still, to 2,200–6,800 cubic meters per hour for 15 minutes, and 26,000–80,000 cubic meters for three hours.
 
For the omicron variant (not distinguishing between sublineages), the ventilation rate hit 5,400–17,000 cubic meters per hour for 15 minutes and 64,000–250,000 cubic meters per hour for three hours.
 
"Without any additional measures, this means the alpha variant requires a ventilation rate some four times aggressive than the ancestral strain," said Bin Zhao, professor at Tsinghua University in Beijing, "while the delta and omicron variants require ventilation rates roughly 20 times and 50 times greater. This is difficult to meet for actual building engineering."