Photo/Illutration People wearing face masks walk across an intersection in the Ginza shopping district in Tokyo on June 10, 2021. (AP Photo)

OSAKA—The probability of infection with the Omicron variant is greatly lowered with distance, mask wearing and other measures, but the strain still spreads more easily than the Delta strain, according to Fugaku supercomputer simulations.

Before conducting the simulations, the team at the Riken research institute estimated that the Omicron variant was 1.5 times more contagious than the Delta variant, based on results of epidemiological research and other sources.

One Fugaku simulation was of a maskless person infected with the Omicron variant who talked to someone for 15 minutes at a distance of 1 meter.

The probability of the variant infecting the other person was around 60 percent on average, but the rate could surpass 90 percent at most, according to the researchers.

When the team conducted the same simulation of a maskless person with the Delta variant, the highest infection probability was just over 80 percent, while the average infection probability was around 50 percent.

If a maskless person infected with the Omicron variant maintained a 2-meter distance, the amount of space between talkers recommended by Japanese authorities, the highest infection probability reached around 60 percent, while the average infection probability was just over 20 percent.

Even if someone infected with the Omicron wore a nonwoven face mask, the highest infection probability reached around 10 percent if the person stayed only 50 centimeters from the person he or she was talking to.

When the team cut the distance to 25 centimeters, the highest infection probability was around 30 percent. Distances of 50 or 25 centimeters are about the space between people on a crowded train or between people whispering to each other in meetings.

However, when the team increased the distance from the mask wearer to 1 meter, the risk of spreading the virus fell to near zero.

The team also conducted a simulation on 16 people, consisting of customers or staff members, at a small restaurant furnished with tables and counters.

If one of the 16 people was infected with the Omicron variant, another person would become infected after an hour if the restaurant only used its original mechanical ventilation system, the research team said.

If the restaurant also used a kitchen duct system and an air conditioner for ventilation, the risk of infection was halved.

If the restaurant also used partition boards, the infection risk was reduced to almost one-third of the level under the original scenario.

Although droplet particles traveled in the restaurant when it used a kitchen duct system and an air conditioner, they accumulated and posed an infection risk in fewer areas inside the facility. This means using a kitchen duct system and an air conditioner can help lower the risk of infection.

“It is important to go back to the basics and to make sure that people take measures against infection, such as keeping a distance from people,” said Makoto Tsubokura, leader of the team and professor at Kobe University. “Also, in order to reduce the risk of infection to the level of that of the original novel coronavirus, we need more measures.”

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The graph shows results of simulations conducted by a team at the Riken research institute to find infection risk of the Omicron or Delta variants of COVID-19 when people infected with these strains don’t wear face masks and talk to other people for 15 minutes. The horizontal axis shows the distance the infected people keep from those they talk to. The vertical axis shows infection probability. The simulations were conducted in three different settings. The solid lines show average infection probability of the Omicron or Delta variants. The dashed lines show the highest or lowest infection probability of these strains. The graph was produced with the help from Toyohashi University of Technology, Daio Paper Corp., Kyoto Institute of Technology, Tokyo Institute of Technology and Kyushu University. (Provided by the Riken research institute and Kobe University)
20220203-fugaku2-L
The graph shows results of simulations conducted by a team at the Riken research institute to find infection risk of the Omicron or Delta variants of COVID-19 when people infected with these strains wear face masks and talk to other people for 15 minutes. The horizontal axis shows the distance the infected people keep from those they talk to. The vertical axis shows infection probability. The simulations were conducted in three different settings. The solid lines show average infection probability of the Omicron or Delta variants. The dashed lines show the highest or lowest infection probability of these strains. The graph was produced with the help from Toyohashi University of Technology, Daio Paper Corp., Kyoto Institute of Technology, Tokyo Institute of Technology and Kyushu University. (Provided by the Riken research institute and Kobe University)

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