Someone at Your Large Gathering Probably Has COVID-19


Our new model projects the chance that within a gathering of random people, there's an active COVID-19 infection.

Bruce Hamory, MD, Ugur Koyluoglu, Terry Stone, and Elizabeth Shakhnovich

4 min read

As we head into Spring, many are hoping that our tremendous accomplishments in vaccination thus far will allow us to gather with our friends and neighbors and begin the return to work, normal business operations, and even event attendance. Many states are embracing this optimism and lifting restrictions, despite warnings from experts pointing to rising cases and the increased spread of more transmissive and dangerous variants.

The Pandemic Navigator team has released a new, publicly available tool that allows users to assess the risk that an indoor gathering with a specified number of random people, on a given date, and in a given US county, will have at least one attendee with an active COVID-19 infection. This can help users ascertain the risk of holding such a gathering. Here are three key takeaways from the analysis:

1. Risk remains high.

Despite a significant drop in cases since the winter holidays, cases plateaued at nearly 65,000 new confirmed cases per day and have recently begun to tick up. This level of active case infection results in 47 percent of counties seeing a risk of more than 50 percent for a gathering of 50 people (as of March 31, 2021).  

2. Keep it small.

If you need to gather indoors, keep gatherings smaller. For example, with gatherings of 20 people, only 10 percent of counties see a risk greater than 50 percent (as of March 31, 2021).

3. Don’t leave it to chance.

This analysis assumes a random selection of county residents, but selection for individuals with specific characteristics (such as vaccination status and a recent negative test) will dramatically reduce the risk of an infected individual attending the event and will help keep everyone safe.

After a dark year, there’s light at the end of the tunnel. It is impossible not to feel optimistic as the weather warms and our daily vaccinations rise rapidly. But it is also important to remember the pandemic is not yet over and the threat of new variants is real. We must remain vigilant, continue to use tools at our disposal (like masking, social distancing, and spending time in the safer outdoors), loosen our restrictions gradually, and (most importantly) continue to vaccinate rapidly.