How quickly can you catch COVID-19?

Throughout the last several months, the US Center for Disease Control has messaged that in order to catch COVID-19 you had to be within six feet of an infected person for fifteen minutes. This was reassuring information. But sadly the US was also perhaps in a difficult place to answer detailed questions about COVID cases, because the contact tracing system has been overwhelmed. The US has also lacked a national COVID tracking app, as many other nations (Australia) have had. Realistically, this would have been a political impossibility to implement in the US, given that even masks have been highly politicized here. So, how realistic was the CDC’s guidance?

The CDC itself pointed to a case in Vermont in which a masked corrections officer was infected with COVID even though he never spent more than a single minute with infected prisoners. Instead, he spent perhaps a total of 17 minutes in a day with them over the course of multiple brief visits, all of which were captured on video. He also wore a mask, gown, and goggles. The prisoners sometimes wore their masks, and sometimes not. After this case, the CDC changed its rules to reflect cumulative exposure. Still, the fifteen minute rule still held. But would new information change these guidelines?

In Korea, contact tracing has been highly effective. It turns out that the combination of a digital tracking app with highly skilled contact tracers has been more successful than either purely digital or human tracing would be. And what Korea has learned -in a remarkable piece of scientific work- is that in one case a high school senior was infected after five minutes of exposure and from twenty feet away. The infection took place in a restaurant (which had video recording) and it turns out that an air conditioning unit was wafting air from an infected person towards the student. The quality of the data that the contact tracers obtained -and the history of how they learned it- is remarkable, and well worth reading.

There is nothing magic that happens at the six feet mark from another person. And being exposed to an infected person indoors can be risky even when the CDC’s old guidelines might make us feel safe. In this case, Korea has given us not only important information, but also let us see the quality of information contact tracing can provide. The key message is that neither six feet of distance, or avoiding more than fifteen minutes of exposure to another person, may be enough to keep you safe from infection, particularly indoors. So indoor dining is probably always unsafe.

Shawn Smallman

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