Before David Lee gathered with his parents for Christmas, he and his family took Covid-19 precautions. They isolated themselves a few days before meeting. His parents, who are more vulnerable because of their age, got the vaccine booster shot, as did Mr. Lee, 43, a photo editor who lives in Toronto. His children, ages 8 and 10, got their first vaccine shot. And they all took rapid tests leading up to the holiday.
“With all the different things added together, it felt like a relatively safe gamble to gather for the holidays,” he said.
Still, he wanted to be extra sure.
So a week before Christmas he used a Covid risk calculator he found on the internet. This one was created by Canada’s National Institute on Ageing, and it asked him questions such as how many people would be at the gathering, how old everyone is and whether everyone had been fully vaccinated.
He plugged in additional information about where they would be meeting (indoors or outdoors) and what they would be doing (talking, eating, singing, hugging). The calculator incorporated information about Covid rates and community spread in Toronto, where the gathering would take place, and then assessed his risk of being exposed to Covid-19 at the event.
He was relieved the answer was low. “If there was a red flag, it would have at least given us pause,” he said. “This tool is about understanding the risk, about having a third party arbiter saying, ‘Maybe this isn’t a good idea.’”
Covid risk assessment calculators are a recent weapon in people’s quest to go about their normal lives while staying safe. Universities, governments and nonprofits have created different versions to help people assess their particular situations.
Each calculator is created differently. The one Mr. Lee used was created by a process named the Delphi Method, in which a group of 20 experts including infectious disease specialists and epidemiologists rated risky behavior — eating inside, for example — on a scale of 0 to 10.
Their responses were aggregated to assign a score to each behavior a user reports (perhaps hugging an unvaccinated person). The team revises the calculator every three months as they get new information about what constitutes risky behavior and different behaviors that can add to or mitigate risk (they recently added rapid testing, for example).
Calculators vary slightly. Some assess your risk of contracting Covid at a particular gathering. Other calculators measure the likelihood of someone arriving with the virus to your event (rather than your chance of catching it) or how likely you are to get Covid in an indoor site like a grocery store or hair salon. Users like them because they provide an objective way to check or justify their decisions.
“Every scenario is different,” said Dr. Samir Sinha, the director of geriatrics at the Sinai Health System and University Health Network in Toronto, who helped created the tool Mr. Lee used. “It’s like being about to call Dr. Fauci and say, ‘You know, Tony, I am going to this event, this is the situation, what do you think?’”
The calculators can ease anxiety in different ways. Kelly Guillemette, 52, a retiree who lives outside of Toronto, found out that events she thought were high risk actually weren’t. “The app made me say, ‘Maybe I am causing myself excess anxiety in my own head?’” she said. “I was having a really, really hard time trusting the outside world.”
Some people have even incorporated these calculators into their day-to-day lives.
“I am using it for every decision I have to make when I leave the house,” said Alison Bergstom, 44, who lives in Cambridge, Mass., and is getting a master’s degree in data science and analytics. She uses a calculator created by the Massachusetts Institute of Technology that assesses the risk of being with other people inside.
Before Thanksgiving, she used a calculator to assess her risk in going to Costco. “To consider how big the store is, how many people will be there, are people going to be wearing masks, are people going to be eating samples,” she said. “I changed my entire schedule around when it said the risk was high. I went Monday morning as soon as it opened so it was less busy and I could go in and out.”
She also crunched numbers before going to a hair appointment. “The app asked how many people would be there and what they would be doing. I realized people would be talking loudly because the hair dryers would be on,” she said. “It showed the risk was quite significant so I decided not to do it.”
(These calculators encourage you to make your most educated guess when filling in the data. For example, if you know a bar checks for vaccine cards at the door you can say with certainty everyone inside is vaccinated. If a bar doesn’t check for vaccine cards, you can infer the data from local vaccination rates.)
Christina Hendriks, 39, who is pursuing a master’s degree in public health and lives in Waynesville, N.C., uses an app that was developed by a team at the University of Oxford every morning. “It’s become part of my routine,” she said. “I run the calculator if we have to go to a doctor’s appointment, go shopping or do in-person banking.”
She said that rather than making her anxious, the calculator empowers her to make informed decisions. When transmission rates are low, she can see the data showing she can resume normal activities with reasonable precautions. When transmission rates are high, she scales back her activities.
The Coronavirus Pandemic: Key Things to Know
The U.S. surge The U.S. record for daily coronavirus cases has been broken, as two highly contagious variants — Delta and Omicron — have spread across the country. The seven-day average of U.S. cases topped 267,000 on Tuesday, according to a New York Times database.
New C.D.C. guidelines Hoping to prevent further disruptions to daily life, the C.D.C. reduced the period that certain infected Americans must sequester to five days from 10. This change applies only to those without symptoms, or those without fevers whose other symptoms are improving.
Staying safe Worried about spreading Covid? Keep yourself and others safe by following some basic guidance on when to test and how to use at-home virus tests (if you can find them). Here is what to do if you test positive for the coronavirus.
Around the world Britain, Denmark, France, Greece and Italy all set records for new daily cases this week. In each country, health officials suspect that Omicron is driving the infections. Globally, thousands of flights were canceled as the Omicron variant began to affect airline crews.
“With the data you don’t feel as trapped or as hopeless,” she said. “There are periods where it shows I need to bunker down for a while, but there are also periods when we can live almost a normal life.”
She equates using the calculator daily to checking the weather, which is the exact attitude scientists want people to adopt, said Kaitlyn Johnson, who helped create a holiday risk estimator as part of her work with the Rockefeller Foundation’s Pandemic Prevention Institute. “In the same way we use weather apps to understand where there is a risk of a hurricane, we want people to be able to monitor their risk of being exposed to a disease,” she said.
Her colleague, Sam Scarpino, who also works at the institute, said he hopes people adopt these calculators to assess all types of health risks — maybe the flu is prevalent or there is a measles outbreak — in the future. “Whether someone is a public health official taking care of their community or someone going on a date, people need tools to translate all this complexity into a decision,” he said. “I think the public is learning to adopt these kinds of tools to make decisions in a little more informed way.”
Some users, however, report feeling more anxious after using them. Nick Rafter, 38, a real estate agent in the Ozone Park section of Queens, was running the numbers before social gatherings or trips away. “It was mostly out of curiosity, not to decide whether or not to do them,” he said. “I wanted to be prepared for what could happen, so I planned ahead. If I got Covid, I could at least say, ‘Well the calculator did say my chances were. …’”
But he soon realized that knowing his risk made his emotional state more volatile. “I started thinking, ‘Maybe I shouldn’t have come? Am I getting infected now?’ and I would have a miserable time and feel anxious,” he said. After he got his booster shot in November, he decided to stop running the numbers, especially if he was going to gatherings anyway. (He did say he may turn back to a calculator in the future. “I’m going on a cruise in February,” he said. “I might see myself using it for that.”)
Some are discovering, thanks to the calculators, that the people around them may not be the best judge of risk. Ms. Bergstom was asked out on a date recently by a scientist who claimed to be cautious and safe. But after he suggested a date, she realized he wasn’t.
“He told me where he wanted to go, and I looked online, and I ran the numbers, and it’s all indoors and very small, and the day and time he invited me out was going to be the most crowded,” she said. “I didn’t even want to suggest something else. I turned him down because I thought his decision making was poor.”
Other people like calculators because they give them neutral, nonemotional data on which to make their decisions (and back them up).
“It’s like having a mediator come in and say, ‘This isn’t a good idea,’” Mr. Lee said. “If your parents want to gather and you don’t, this takes away the emotions of it. It’s just medical advice saying, ‘This is not a good idea.’” Ms. Johnson has had multiple friends reach out to her and say they are using it to explain to their families the risk of gatherings.
Of course, some people looking for a way out of a social function don’t always get the results they are looking for.
“Some of the comments we get are hilarious,” said Dr. Sinha, one of the creators of the calculator in Canada. “I had one person saying before the U.S. Thanksgiving that he didn’t want to visit his in-laws, and he was hoping the risk calculator would say it was a high-risk event. Unfortunately it was low.”