Dry indoor spaces 'perfect conditions' for Covid spread in winter, supercomputer finds

A humidifier in the home or office could help prevent spread of contagion, Japanese research says

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The world's fastest supercomputer has calculated a heightened risk of coronavirus spread in dry indoor spaces – pointing to a rise in cases in colder climates during the winter months.

The processing power of Japan's Fugaku supercomputer has been used in the fight against the pandemic for months.

Its latest findings indicated that humidity can have a large effect on the dispersal of virus particles, suggesting humidifiers may limit infections during times when window ventilation is not possible.

A study by Japanese research institute Riken and Kobe University tasked Fugaku with modelling the emission and flow of virus-like particles from infected people in a variety of indoor environments.

Air humidity of lower than 30 per cent resulted in more than double the amount of aerosolised particles compared to levels of 60 per cent or higher, the simulations showed.

The study also suggested that clear face shields are not as effective as masks in preventing the spread of aerosols.

The Riken research team, led by Makoto Tsubokura, has used the Fugaku supercomputer to model contagion conditions in trains, work spaces, and classrooms.

The simulations showed that opening windows on commuter trains can increase the ventilation by two to three times, lowering the concentration of microbes.

“People’s blind fear or unfounded confidence against the infection of Covid-19 is simply because it is invisible,” Dr Tsubokura said.

Earlier this month, the US Centres for Disease Control and Prevention updated its guidance to say coronavirus can linger in the air for hours.

The CDC had not made a direct link about the role airborne transmission is playing in the spread of the virus.

But the public health agency's new advice said aerosolised virus particles can, and do, infect others under certain circumstances.

The capacity of coronavirus to spread through minuscule droplets, which float in the air long after an infected person coughs, breathes, or sneezes, was noted by authorities in China in February, very early in the outbreak.

Circumstances where confirmed airborne transmission has occurred, according to the CDC, include enclosed spaces where people were exposed shortly after the infected person left.

Aerosolised transmission has also occurred when infected people were shouting, singing or exercising, which increased the concentration of “suspended respiratory droplets in the air space”.

In addition, inadequate ventilation can increase the risk of airborne transmission by allowing the build-up of suspended small respiratory droplets and particles, the CDC said.

The agency said most people became infected by inhaling large droplets through close contact with sufferers.

When it is fully operational next year, experts are hoping the Fugaku machine will be able to help narrow the search for effective treatments for coronavirus.

The computer, which fills a room, is housed in the city of Kobe and is named after Mount Fuji – Japan's often snowcapped highest mountain and an active volcano.