closet-keys:

A very pertinent case with regard to understanding the dynamics of indoor transmission was a choir rehearsal in Washington State, in the United States, in March. Only 61 of the 120 members of the choir attended the rehearsal, and efforts were made to maintain a safe distance and hygiene measures. But unknown to them, they were in a maximum risk scenario: no masks, no ventilation, singing and sharing space over a prolonged period. Just one infected person passed the virus on to 53 people in the space of two-and-a-half hours. Some of those infected were 14 meters away, so only aerosols would explain the transmission. Two of those who caught the virus died.

After studying this outbreak carefully, scientists were able to calculate the extent to which the risk could have been mitigated if they had taken measures against airborne transmission. For example, if masks had been worn, the risk would have been halved and only around 44% of those present would have been affected as opposed to 87%. If the rehearsal had been held over a shorter period of time in a space with more ventilation, only two singers would have become infected.

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In summary:

Indoors with social distancing/limited capacity: HIGHLY contagious

Indoors with social distancing/limited capacity with everyone wearing masks correctly: still almost half present would be infected

Indoors with social distancing/limited capacity, with everyone wearing masks correctly, for only one hour, with ventilation: a few people will be infected

Outdoors, with masks and social distance: ideal scenario to prevent spread

Published October 28, 2020