On Thursday, June 25, 2020, California saw its biggest spike in COVID-19 cases since the pandemic began in March, with more than 7,000 new cases confirmed. The increase in confirmed cases comes after citizens have endured months of shelter in place orders, the toll has on the health and financial security of millions steep. Why are cases spiking and what can be done to bend the curve of the pandemic in California? Here, Stanford Law Professor Michelle Mello — also a professor of medicine at Stanford Health Policy — answers these and related questions.

Was California’s “shelter-at-home” (SAH) order effective at flattening the curve of COVID-19? Projections for the state were very gloomy in early March. But we did not hit the worst-case scenarios and the outlook for the state seemed good back in early May.

There is considerable evidence that shelter-at-home and business closure orders, though very burdensome on people and the economy, were successful in flattening the curve. You can see that just by looking at data plots like these that show cases slowing as states implemented orders beginning in late March. There have also been several well-designed studies using mobility data from cellphones that have linked these orders to lower mobility and reduced COVID-19 cases and deaths. From a research perspective, the fact that states and counties entered different orders at different times created a natural experiment that has allowed researchers to isolate the effects of the orders.

Does the recent surge in cases correlate with the state’s opening up from SIP?

Controlled studies haven’t yet examined the reopening period, but the data certainly point in that direction. Because the Bay Area has maintained its health orders longer than the state’s other large metropolitan area, Los Angeles, there is natural variation within California that researchers will undoubtedly exploit to try to confirm that. Comparing case counts and hospitalizations in those two areas is quite striking.

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