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Here’s how long it takes to catch COVID if you’re in a room with someone who has it

Published Dec 1st, 2020 5:35PM EST
Image: Fabian/Adobe

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  • Researchers from MIT put together a website that reveals how long it takes to catch the coronavirus when in a room with someone who has it.
  • The risk of transmission is dependant on a few variables (room size, mask-wearing) that users on the website can tweak to fit their environment.
  • Indoor gatherings are disproportionately responsible for coronavirus transmissions.
  • If you find yourself at an indoor gathering, it’s imperative to wear a mask and to adhere to social distancing guidelines.

Though the coronavirus can spread more readily than the flu, the reality is that simply being in the same room as someone who has the virus doesn’t automatically mean you’re going to contract it yourself. Even when indoors — where the coronavirus is more likely to spread — the virus’ ability to spread from one person to another depends on a variety of factors such as air circulation, whether or not people are wearing masks, social distancing, the viral load of the infected person, the size of the indoor space, and more.

In light of the above, a pair of researchers from MIT recently used mathematical models to anticipate the likelihood of someone contracting COVID-19 when in the same room as someone who already has it. Even more helpful is that the researchers used all of their findings to create a website where users can specifically enter in several variables to help them determine the risk associated with an indoor gathering.


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The website can be viewed over here and is, without exaggeration, fascinating to play around with. Aside from picking from a list of indoor environments like a restaurant, church, or suburban home, users can also specify the square footage of a given room, the ceiling height, the ventilation system, and the humidity. With respect to human behavior, users can specify whether or not people are talking quietly or loudly, what percentage of people in the room are wearing masks, what type of masks people are wearing, and even the risk tolerance of people in the room.

As an illustrative example, here is a scenario I plugged into the site: The environment I chose was a 500 square-foot room with 10-foot high ceilings. As far as human behavior, I indicated that people would be standing, talking at a normal volume, and that 50% of the people in the room would be wearing masks. Based on the above, the site relayed back that 2 people could be in the room for 2 hours without a significant risk of catching the coronavirus. When I changed the setting to make it so that no one in the room was wearing a mask, the website indicated that someone would likely contract the coronavirus after 45 minutes.

Clearly, no one at this point should be planning or attending any type of indoor gathering given how rapidly the coronavirus is spreading. Still, if you’re planning to head back home for the Christmas holiday, it’s probably a smart idea to check the website out, plug in the requisite variables, and get a gauge as to how safe things will be.

In an effort to approximate a typical holiday gathering, I decided to look at the risk of transmission in a 2,000 square foot house with standard AC and closed windows. Assuming a gathering of 5 people, and assuming that no one wears a mask indoors, the website relays that it would take only 3 hours for someone to contract the coronavirus. A gathering of 10 people changes the time frame to two hours.

Looking ahead, we can only hope that promising vaccines from Pfizer and Moderna can help us move past the coronavirus pandemic over the next few months. Incidentally, Moderna today said that its coronavirus vaccine is 100% effective when it comes to preventing severe coronavirus symptoms from kicking in. In a best-case scenario, Dr. Fauci has said that life might return back to normal by next summer.

Yoni Heisler Contributing Writer

Yoni Heisler has been writing about Apple and the tech industry at large with over 15 years of experience. A life long expert Mac user and Apple expert, his writing has appeared in Edible Apple, Network World, MacLife, Macworld UK, and TUAW.

When not analyzing the latest happenings with Apple, Yoni enjoys catching Improv shows in Chicago, playing soccer, and cultivating new TV show addictions.