With so many states now deep in crisis, the signs of provisional success in the Seattle area offer a lesson for other cities and regions that are just beginning to see the onset of the coronavirus: Early and aggressive action to contain the spread may help lower the trajectory of a virus that could otherwise overwhelm health systems.

Officials in Washington State first began to plead with people to keep their distance from one another at the end of February, after discovering that the virus had infected people in the Seattle area with no known exposure or history of foreign travel, followed by an outbreak at a suburban nursing home now linked to dozens of deaths.

Within a week, the county was asking organizations to consider postponing large events and for people to work from home if possible. People over 60 were encouraged to remain indoors. Some of the region’s major employers, including the headquarters campuses of Amazon and Microsoft, responded by encouraging workers to work from home, quieting workplace hubs that would otherwise be bustling during commutes and lunchtime.

The demographics of those workplaces, with tens of thousands of tech workers who were able to telecommute, may have given the region an early edge in keeping people separated. Perhaps the city’s social norms helped, too, as local residents have long had a reputation for keeping to themselves or within circles of longtime friends — a phenomenon often explained to newcomers as the Seattle Freeze.

Ms. Durkan said the region also benefited from a robust network of researchers who were able to do early modeling to assess the reach of the virus in the community. Without that, she said, policymakers may not have taken the drastic steps to shut down the city as quickly as they did.

The region has also benefited from more widespread testing than most states, helping feed data to the researchers’ models and give a sense of how much infection might be missed.

After scientists found evidence that the virus had been circulating weeks before some of the earliest cases were identified, researchers from local groups, led by the Institute for Disease Modeling, began looking at what it would take to slow the progress of the virus. On March 10, they developed projections showing that significant changes in human-to-human contact would be needed to avert hundreds more deaths by April 8.