A UCSF doctor did some math to estimate the number of lives the San Francisco Bay Area may have saved by jurisdictions acting quickly and residents following strict shelter-in-place orders.

Dr. George Rutherford, a professor of epidemiology and the head of the division of infectious disease and global epidemiology, believes some 34,000 to 44,000 lives have been saved partially through the region’s early action, such as San Francisco Mayor London Breed issuing a state of emergency on February 28.

Rutherford pointed out that Breed’s declaration nudged people to start staying home nearly three weeks before the shelter-in-place order was issued, dramatically limiting people’s movement.

How did Rutherford get to these numbers? First, he looked at the worst-case scenario forecasts for deaths in the United States if no precautions were taken.

A top disease modeler at the U.S. Centers for Disease Control and Prevention forecast that the U.S. could see as many as 1.7 million deaths. The C.D.C. didn’t release the number to the general public, but the New York Times obtained screenshots from a presentation done on a phone conference and verified the data with scientists on the call. What’s more, a model from the Imperial College of London forecast 2.2 million Americans could die as a result of the coronavirus pandemic if people went on with their daily lives as disease spread.

Rutherford figured the six Bay Area counties that issued shelter-in-place orders on March 16 — Alameda, Contra Costa, Marin, San Francisco, San Mateo and Santa Clara — make up about 2% of the U.S. population, considering these counties have about 6.6 million residents compared to the 328.2 million U.S. population.

Two percent of 1.7 million is 34,000 and of 2.2 million is 44,000; these numbers provide a very rough estimate of the number of deaths that could have occurred if no precautions were taken, according to the C.D.C. and Imperial College in London. In reality, Rutherford said, “We’ve had 200 deaths so far. That’s the delta. That’s the difference. That’s a lot.”

The reservation site Open Table is one indicator offering additional proof that people in the Bay Area were staying home earlier than those in other parts of the country. Rutherford said reservations dropped dramatically in San Francisco after February 28 while in Los Angeles and New York, the data shows people continuing to go out.