California appears to be flattening the curve - but residents must keep social distancing for at least another month, experts say

• Coronavirus case numbers in California indicate that the state is beginning to "flatten the curve."
• California was the first state in the country to issue a stay-at-home order.
• Cases in the state were doubling about every 3.5 days at the end of March. Now, they're doubling every week.
• But the state still has a backlog of about 14,000 tests to process.
• The rate of case growth will only continue to slow if Californians and other Americans maintain social distance for another month.
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California was the first state in the US to issue a stay-at-home order. About three weeks later, the effort seems to be working.

"Let me give you a sense of optimism, in terms of the curve in California bending: It is bending, but it's also stretching," Gov. Gavin Newsom said at a news conference on Wednesday.

Restrictions on movement aim to promote social distancing and "flatten the curve" of the coronavirus outbreak - slow the spread of the virus, in other words, to reduce the strain on the state's healthcare system. California is seeing the impacts of these policies after a delay, since a given day's number of new confirmed cases generally reflects infections contracted about two weeks earlier. (The virus' average incubation period is five days, and symptoms worsen over the first week.)

As of Thursday, the number of confirmed cases in California was around 19,000; just over 500 people have died. Roughly 2,700 people are hospitalized in the state, with about 1,150 in intensive-care units.

These numbers are far lower than projections in mid-March anticipated - so much lower, in fact, that one model moved the date of the expected peak of California's outbreak up two weeks, to April 14. The model, from the University of Washington's Institute for Health Metrics and Evaluation, also estimates that the state's current number of hospital beds, ICU beds, and ventilators will be able to meet the needs of coronavirus patients.

But it's not all rosy: California is struggling with a backlog of tests, faces a risk of infections from residents of other states, and must find a way to keep social-distancing measures in place sustainably for at least another month.

California's early stay-at-home order made a difference

Nine counties in the Bay Area were the first in the US to issue a "shelter-in-place" order. Beginning March 17, residents were told to stay inside their homes as much as possible and leave only for essential needs, such as to buy groceries or medicine.

Gov. Newsom issued the statewide order two days later, and projected that 56% of the population would be infected with the virus over an eight-week period - about 22.5 million people. At that point, California had confirmed 1,067 coronavirus cases and 19 deaths.

But John Swartzberg, a professor of infectious diseases at UC Berkeley, told Business Insider that the early shutdowns might have saved California from the worst projected outcomes.

"Other states followed, but they followed like Europe followed - somewhere between five and seven days later," he said. "It doesn't sound like a lot, but it is a lot when you look at how fast the numbers of cases are increasing."

Flattening the California curve

As is true across the US, California's official number of cases is almost certainly an undercount. Reports from across the state show that tests have primarily been done in the most severe cases since testing capacity has been limited nationwide due to errors and delays in the federal rollout. So California's numbers likely leave out many mild and asymptomatic cases, which research suggests account for the vast majority. The state has conducted about 159,000 total tests as of Thursday, according to the COVID Tracking Project.

But it's still waiting on the results of about 14,000 of those tests.

"The reporting of the results of testing and the reporting of patients who are sick is not giving us the full picture," Swartzberg said. "So when we try to do modeling, at least one arm and maybe half of another one are tied behind our backs."

Still, the numbers we do have suggest rate of growth of new cases in California is slowing, even as testing ramps up.

On March 26, cases in California were doubling around every three to four days, Dr. Mark Ghaly, secretary of the California Health and Human Services Agency, told the San Jose Mercury News. But as of Monday, the state was seeing a 7.6% day-over-day growth in new cases, and it took all of last week for the number of cases to double, according to the Mercury News.

Swartzberg said it's still too early to make assumptions about the success of the state's response, though.

"The virus doesn't respect borders," he said, noting that there's a risk people bring it in from other states.

Officials and health experts agree that for California to maintain its initial curve-flattening success, residents must continue to heed the stay-at-home order and practice social distancing.

"If we look like other countries' experience, you'll then see a plateau and then see it start to drop," Swartzberg said. "So I would say that we could confidently say that we have succeeded in flattening the curve probably sometime in early- to mid-May."

Katie Canales contributed reporting.

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