Home / Health / Japan has long accepted COVID’s airborne spread, and scientists say ventilation is key

Japan has long accepted COVID’s airborne spread, and scientists say ventilation is key

Tokyo – Under pressure from the scientific community, the World Health Organization acknowledged last week airborne transmission of “micro-drops” as a possible third cause of COVID-19 infections. For many researchers in Japan, the assumption felt anticlimactic.

This densely populated country has been working for months on the assumption that small, “aerosolized” particles in cramped environments turbocharge the spread of the new coronavirus.

Very few diseases – tuberculosis, chickenpox and measles ̵

1; have been assessed to be transmissible through aerosols. Most are spread only through direct contact with infected persons or their body fluids or contaminated surfaces.

The WHO has still refused to confirm aerosols as an important source of new coronavirus infections, saying more evidence is needed. But scientists are keeping the pressure on.

“If the WHO recognizes what we did in Japan, maybe in other parts of the world, they will change (their antiviral practices),” said Shin-Ichi Tanabe, professor of architecture at Japan’s prestigious Waseda University. He was one of the 239 international researchers who together wrote an open letter to the WHO calls on the UN agency to revise its guidelines on how to stop the spread of the virus.

Scientists flag airborne coronavirus spread


Large droplets pushed out through the nose and mouth tend to fall to the ground quickly, explained Makoto Tsubokura, who runs the Computational Fluid Dynamics lab at Kobe University. For these larger respiratory particles, social distance and face masks are considered to be adequate protective measures. But in rooms with dry, old air, Tsubokura said his research showed that people who cough, sneeze and even talk and sing, emit small particles that defy gravity – can hang in the air for many hours or even days and travel the length of a room.

The most important defense against aerosols, Tsubokura said, is to dilute the amount of virus in the air by opening windows and doors and ensuring that plumbing systems circulate fresh air. In open offices, he said partitions must be high enough to prevent direct contact with large drops, but low enough to avoid creating a cloud of virus-heavy air (55 inches or head height). Small desk fans, he said, can also help spread the airborne viral density.

For the Japanese, the latest WHO adoption confirmed at least one strategy the country adopted in February, when residents were told to avoid “the three Cs” – confined spaces, confined areas and close conversations.

A graphic created by the Japanese government urges citizens to avoid confined spaces, confined areas and close conversation – “Three Cs” – to minimize the spread of the new corona virus.


After a calm, new infections – mainly among younger Tokyo residents – have recently resurfaced and topped 200 in four straight days, before falling back to 119 on Monday.

Aggravatingly, new cases emerge not only in notoriously cramped and cramped nightlife, but also in homes and workplaces, prompting the national government to consider asking companies to shut down again in the larger metro region. The authorities are keen to prevent a correspondingly powerful force in serious cases and deaths, which have so far been low.

Tsubokura, who also serves as a leading researcher for the government institute RIKEN, has pushed simulations of Japan’s new Fugaku supercomputer study how to protect against airborne transmissions in subways, offices, schools, hospitals and other public spaces.

The Fugaku supercomputer is seen at Kobe, Japan’s office in the Riken Center for Computational Science, which is part of the government-run research institute RIKEN. From June 2020, Fugaku was ranked as the world’s fastest processed supercomputer.


His computer model of riders on Tokyo’s congested Yamanote train line (watch the animation at 7:15 minutes in this video) illustrated how airflow stagnates on packed trains with closed windows, as opposed to free-flowing air on wagons with few passengers and open windows. He suggests that the windows are always kept open to mitigate the risks when the trains are filled.

But Japan’s incredibly congested train, he argues, is probably not as risky as his model suggests. “It’s very crowded, and the air is bad,” Kurokabe said. “But no one talks, and everyone wears a mask. The risk is not that high.”

Even going on a crowded subway train – if windows are kept open, as they are in Japan these days – “is much safer than a pub, restaurant or gym,” said Waseda University’s Tanabe.

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Masking of the nose and mouth is all the more important, he said, because his research shows that men touch faces up to 40 times an hour. (He said that women who are more likely to make up are less facial.)

“Non-woven (surgical) masks are high-performance, but fabric works as well – it’s much better than nothing,” he said. “The only way to avoid leakage (of drops) is to tightly mount the mask.”

A digital simulation created by Japan’s supercomputer Fugaku models the spread of microparticles, which can carry the new corona virus, by (top, left to right) a person coughing while wearing no mask, a poorly mounted non-woven mask and a well – mounted non-woven mask, and on the bottom the same modeling for a person who speaks normally.


The mask features and ventilation directives help the Japanese reopened concert halls, baseball stadiums and other arenas. As of last Friday, such places can receive up to 5,000 patrons.

Tanabe will rely on Japan’s new Fugaku supercomputer – recently declared the world’s fastest – to plan optimum ventilation system efficiency.

“It’s like predicting a typhoon,” he said, noting that forecasts for both extreme weather and airflow through narrow trains rely on the same equations to calculate fluid dynamics.

An illustration, including in an article on the spread of aerosolized coronavirus particles in confined spaces in the journal Environment International in September 2020, shows various methods recommended to dilute the concentration of virus-loaded microparticles in the air.

Environment International / Science Direct

In an article that will be published in the September issue of the scientific journal Environment International – Because schools and other public facilities are struggling to reopen – Tanabe and other experts argue that protecting indoor spaces can be done relatively easily and cheaply by avoiding congestion and maintaining the flow of fresh air.

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