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Face shields not 'a guaranteed alternative' to masks to block virus: Japanese scientists

Health minister Norihisa Tamura is seen wearing a face shield amid a call for the public to use shields when dining, during a news conference at the Diet building on the morning of Nov. 20, 2020. (Mainichi/Hidenori Yazawa)

TOKYO -- A team of scientists in Japan is urging people to "wear masks whenever possible" to prevent the spread of the coronavirus as the number of new infections in the country continues to increase, while warning about the use of face shields as an alternative.

    The most basic preventive measure a person can take to prevent infection is to wear a face mask. Japan's health minister Norihisa Tamura recently urged the public to wear masks while dining and at parties.

    "When alcohol is involved and when there are many people (at a gathering) people tend to become loud, which spreads droplets. The risks of transmission increase as the period of a gathering becomes longer," he said.

    A team of scientists made up of members of institutions including Japan's major research institute Riken and Kobe University has already shown in August that face masks prevent droplets from spreading. A simulation with the supercomputer "Fugaku" on how human droplets spread when a person coughs showed that both non-woven fabric masks and cloth masks blocked some 80% of droplets.

    Tamura also called on the public to use face shields when dining with others to prevent the spread of the coronavirus, wearing one himself during the Nov. 20 press conference. However, the team of scientists presented simulation results from Fugaku in October which showed that while face shields are effective in blocking large droplets, smaller particles can escape in large volumes through openings. The team warns that the face shields are "not guaranteed" to function as an alternative to masks.

    (Japanese original by Yuki Ogawa and Hidenori Yazawa, Lifestyle and Medical News Department)

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