A new analysis suggests that schools and colleges, large companies and other organizations that want to keep themselves safe with frequent mass testing should think beyond their own personnel.

By dedicating a substantial portion of their tests to people in the surrounding community, they can reduce the number of Covid-19 cases among their members by as much as 25 percent, researchers report in a new paper, which has not yet been published in a scientific journal.

“It’s natural in an outbreak for people to become self-serving, self-focused,” said Dr. Pardis Sabeti, a computational biologist at Harvard University and the Broad Institute who led the analysis. But she added, “If you’ve been in enough outbreaks, you just understand that testing in a box doesn’t makes sense. These things are communicable, and they’re coming in from the community.”

The study has “really profound implications, especially if others can replicate it,” said David O’Connor, a virologist at the University of Wisconsin, Madison, who was not involved in the analysis but reviewed a draft of the paper.