Chiu’s analysis shows California’s strict shelter in place efforts appear to be working.

Over half of the 50 SARS-CoV-2 virus genomes his San Francisco-based lab sequenced in the past two weeks are associated with travel from outside the state. Another 30% are associated with health care workers and families of people who have the virus.

“Only 20% are coming from within the community. It’s not circulating widely,” he said.

That’s fantastic news, he said, indicating the virus has not been able to gain a serious foothold because of social distancing.

It's like a wildfire, Chiu said. A few sparks might fly off the fire and land in the grass and start new fires. But if the main fire is doused and its embers stomped out, you can kill off an entire strain. In California, Chiu sees a lot of sparks hitting the ground, most coming from Washington, but they're quickly being put out.

An example was a small cluster of cases in Solano County, northeast of San Francisco. Chiu’s team did a genetic analysis of the virus that infected patients there and found it was most closely related to a strain from China.

At the same time, his lab was sequencing a small cluster of cases in the city of Santa Clara in Silicon Valley. They discovered the patients there had the same strain as those in Solano County. Chiu believes someone in that cluster had contact with a traveler who recently returned from Asia.

“This is probably an example of a spark that began in Santa Clara, may have gone to Solano County but then was halted,” he said.

The virus, he said, can be stopped.