A free app from Brown University researchers reveals your risk of getting COVID-19 based on your activity and zip code

• Public guidance about how to lower your risk of exposure to COVID-19 isn't always clear.
• So physicians and researchers at Brown created an app to help Americans determine the risks of various activities.
• The app relies on six metrics, including ZIP code and the type of activity (like church service, mall trip, or gym workout).

As doctors, Megan Ranney and Liz Goldberg were used to fielding health-related questions from friends and family. But during the pandemic, they've gotten more inquiries than ever before.

"Dr. Goldberg and I were having a discussion about how many of our friends were asking us: Is it safe to do this? Is it safe to do that?" Ranney, director of the Brown University Lifespan Center for Digital Health, told Business Insider. "We said, 'Well, there's science behind this. We can put this together into an algorithm and make it really easy for people.'"

In the fall, Ranney and Goldberg released MyCOVIDRisk, an app that allows users to calculate their risk of contracting COVID-19 based on their activity and location.

The app relies on six key metrics: ZIP code, whether the activity in question is indoors versus outdoors, the type of outing (like a church service, mall trip, gym workout, etc.), a person's duration of stay, crowd size, and the degree of mask wearing. Based on that, it evaluates risk on a scale of "very low" (less than 0.00001% risk of getting infected) to "very high" (a more than 5% risk of getting infected).

No algorithm is perfect, but Ranney said the app draws on research from the University of Colorado Boulder and Georgia State University.

"That first value of what's your local rate of community rate of COVID is probably the most important, because you could be in an indoor gym with 15 other people for two hours, and if there's no COVID in your community, you're not going to catch COVID," Ranney said.

Unfortunately, she added, most ZIP codes across the US have high transmission rates at the moment. COVID-19 cases have risen dramatically since September, making this fall-winter surge the largest yet. New daily cases reached an all-time peak of nearly 225,000 on Thursday.

Daily hospitalizations have also skyrocketed, topping 100,000 for the first time on Wednesday. On average, the number of people dying each day has risen 43% in the last two weeks.

"Right now in this country, the vast majority of indoor activities are high-risk," Ranney said.

How to lower your risk of a coronavirus infection

The app's interface takes less than a minute to fill out. Users adjust a dial to reflect the size of their gathering and duration of the activity, then click on icons that indicate the percentage of people wearing masks.

Once this information is added, users get a result:

Ranney said there are certain activities that will almost always turn out to be high-risk.

"There's really nowhere in the United States right now that you could get together five people unmasked for a dinner indoors and not have it be high-risk," she said. "Maybe Hawaii."

But the app isn't meant to suggest that people should lock themselves at home entirely, she added.

"There are the extremists on both sides: the people who insist that they can do anything and that there's no risk, and then the people who say, 'You know, you just have to stay locked up in your house for a year,'" Ranney said. "Neither one of those are completely accurate."

Some users, she said, may want to find out how to lower the risk of an activity by adjusting the number of people or moving outdoors.

"If you say, 'Listen, I really want to see my family. I can't stand the fact that I haven't seen them for a month.' Well, how can you see them safely?" Ranney said. "It allows people to do the things that are necessary for their mental and physical health while also helping to protect them from making unsafe choices."

Ranney said she recently heard from a user whose family was in a heated discussion over whether to attend an indoor theater performance. The user's wife thought the activity was safe, but the app said otherwise - so the family opted out.

The app leaves out a few variables

MyCOVIDRisk comes with some additional parameters: Before users start, they must verify that they live in the US and aren't experiencing any COVID-19 symptoms. The activities are also limited to roughly a dozen choices.

"There are some things that we purposely did not put into the app because they are so difficult at this point to model accurately," Ranney said.

That includes the risk of visiting doctors' or dentists' offices, since these indoor environments may be surprisingly low-risk if they have proper ventilation and enforce masks and social distancing.

The app also doesn't model the risk of activities for children under 13.

Kids represent around 7% of confirmed coronavirus infections in the US - the lowest of any age group, according to the Centers for Disease Control and Prevention. But pediatric coronavirus cases can be difficult to track, since they're often mild or asymptomatic. Plus, scientists still aren't sure whether kids are less likely to transmit the virus than adults are.

When local guidance isn't clear

The coronavirus spreads like many other viruses, via droplets or smaller airborne particles called aerosols. For that reason, scientists often rely on one question to evaluate risk: How may people are sharing air? That's what the app seeks to assess.

It's also meant to give people data-backed guidance, since the evolving nature of research about the virus and misinformation promoted by some local and federal leaders has made it challenging for many people to evaluate their risk on a case-by-case basis.

"There's been very little consistent and accurate communication from our federal leadership about what puts people at risk of getting COVID," Ranney said. "Some states have done a decent job of communicating that, but those are in the minority and there's a lot of conflicting information out there. It makes it really tough for even people who try to pay attention to the science, and to the news, to figure out what is safe and what isn't."

For example, it took months for scientists to determine whether aerosol transmission was possible, and more data over time also showed that masks are highly effective at blocking respiratory droplets and aerosols. On top of that, President Donald Trump has falsely compared the coronavirus' threat to that of the seasonal flu and suggested that mask-wearing was unnecessary.

Trump also pushed for schools and businesses to reopen in the summer, as COVID-19 cases were still climbing, leading many states to allow gyms, movie theaters, and restaurants to resume indoor operations.

"You might read, 'Well, it's unsafe to be indoors without a mask,' but then you also know that your state allows restaurants to be open and allows weddings to happen," Ranney said. "So even if you're in a state with good public-health messaging, the policies sometimes conflict with what you're hearing."

Her tool is meant to cut down on the guess work.

"Every time you want to do something, if you have to go through this calculation in your head of how safe is it, that's exhausting," she said. "At some point, it's going to fatigue people and make them just say, 'Forget it. I'm going to go do this because I want to.' That was the motivation for creating the app."