How Infectious Was Your Thanksgiving Dinner?

This MIT-developed app will help you figure out whether to worry or carry on.

Six feet isn’t always enough. Depending on whether you’re indoors, outdoors, wearing a mask, wearing a mask properly, talking, yelling, or whispering, the chance of transmitting airborne COVID-19 particles fluctuates. 

That’s why two MIT professors teamed up with a recent Cornell graduate to make an app that can help you estimate how long it should be safe to stay indoors, assuming there’s one person with COVID-19 in the room. This model, created by John W. M. Bush, Martin Z. Bazant and Kasim Khan simulates a variety of factors: the size of the space, the type of ventilation available, the humidity level of the air, and the personal decisions the people inside are making — namely, whether or not you’re wearing a mask.

“The current revival of the world’s economy is being predicated on social distancing, specifically the Six-Foot Rule, a guideline that offers little protection from pathogen-bearing aerosol droplets sufficiently small to be continuously mixed through an indoor space,” Bush and Bazant wrote in the abstract of their research article.

Let’s say you invited four people over for a Friendsgiving dinner. Everyone crowds into the dining room, which is about 200 square feet large. You and your guests aren’t wearing masks because you want to dig in, but you’re staying six feet apart. There’s holiday music playing, wine is being passed around, and in general, people are in good spirits and speaking loudly. But none of you realize that someone in that room has the novel coronavirus. 

Based on this model, it’s only safe for you and your four guests to be in that room together for 20 minutes. That’s about enough time to carve and serve the turkey. 

Another hypothetical scenario: Planning a Thanksgiving dinner is a lot of work, so you and your partner decided to eat out at a fancy FiDi restaurant instead. This place was particularly large — about 5,000 square feet. And, in this imaginary scenario, indoor dining is still open at 25 percent capacity, so this imaginary restaurant will be seating about 50 people. The level of “mask fit/compliance” is at about 25 percent, because while the waiters and chefs and other servers are wearing their masks, the diners are taking them off to eat and to snap a photo for Instagram. 

Based on this model, it would have been safe for about 66 minutes, assuming there was somebody in the room with COVID-19. Is that enough time to order drinks, finish an entree, and get the check?

Unfortunately, there is no “outdoor” mode on the app, so you won’t be able to precisely model any patio gatherings or parklet dinners you may have attended in the past week. (Although there is an option to simulate a large indoor space with open windows and strong ventilation). 

Of course, this is just a guide based upon two researchers’ work and estimates. In the real world, there is no magical timer we can watch to know with certainty just how likely we are to have unwittingly transmitted or contracted COVID-19.

Still, the more we learn about this virus — from scientists and from analyzing our own lived experience — the better we can assess our risk at any given time and make informed decisions that will keep us and our loved ones safe.

And, although it should go without saying, we’ll say it anyway: if you’re experiencing symptoms of COVID-19 or even if you’re just wracked with guilt over that close-quarters heart-to-heart you allowed yourself to have with grandma, there are many testing options available.

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