California last week reported the lowest number of new Covid-19 cases in the nation, suggesting that the state may be turning the tide against the recent delta surge. Here's how—and why experts remain cautious going forward, especially in the face of a potential resurgence in cases during the colder months.

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California sees lower rate of new cases than any other state

CDC last week ranked California's current coronavirus case rate as the lowest in the United States, the New York Times reports.

According to a Los Angeles Times analysis of state public health data, California recently reported around 9,800 new cases a day for the week ending Sept. 10—a 27% decrease from the 13,400 cases a day for the week ending Aug. 27.

Over the same period, several areas in the state—including the San Francisco Bay Area, Southern California, the Greater Sacramento area, San Joaquin Valley, and rural Northern California—reported similar declines in the weekly number of cases.

Covid-19 hospitalizations have fallen statewide by around 10% in recent weeks, the Washington Post reports. Southern California and the San Francisco Bay Area reported the largest decline in hospitalizations at 24%, while the Greater Sacramento Area and rural Northern California reported declines in hospitalizations of 13% and 14%, respectively.

Vaccinations, safety measures likely behind the decrease

According to several experts, the state's "aggressive" push for vaccination, along with mask mandates and a public largely receptive to these mitigation measures, likely helped reduce the number of new cases, the Washington Post reports.

For example, California Gov. Gavin Newson (D) mandated Covid-19 vaccinations for state employees and workers in high-risk settings. Large cities, such as Los Angeles and San Francisco, have also begun requiring proof of vaccination for indoor venues, such as restaurants and gyms. Several of the state's most populous counties also reinstated indoor mask mandates as the delta variant spread, according to the Post.

Currently, more than 82% of Californians ages 12 and older have received at least one dose of a Covid-19 vaccine—a figure that only nine only states have beat, the Times reports. In addition, more than 57% of state's population is fully vaccinated, which is higher than the national average.

"California, as compared to many other states in the nation, took rapid steps to recognize the extent of the problem and to apply more covid control measures," said Robert Kim-Farley, an infectious disease expert at the University of California, Los Angeles Fielding School of Public Health. "I think if California had not taken these steps to curb transmission, we could have ended up with much higher levels."

In addition, John Swartzberg, an infectious disease expert at the University of California, Berkeley, said the state's early efforts in issuing safety measures likely helped it enact later restrictions to limit the spread of the virus. For example, while CDC loosened its masking guidance in May as cases were plummeting around the country, California health officials waited another month before lifting the state's mask mandate.

"California very wisely deferred [lifting the mask mandate] for a month," Swartzberg said. He added that while the decision did not prevent a resurgence in cases, he believes that it "helped [the state] going into the delta pandemic."

Separately, Howard Forman, head of the health care management program at the Yale School of Public Health, said, "They remain an overall high vaccination state and have allowed for more local autonomy over non-pharmaceutical interventions, including excellent testing levels."

"It's never just one thing," Forman added. "But I think they have truly managed this better than most states."

Experts still urge caution going forward

Although California has seen an overall decrease in coronavirus cases, it still faces several challenges as it continues to try to contain the spread of the virus.

According to the Post, while infections have decreased in California's most populous areas over the past few weeks, they remain high in the Central Valley and parts of the rural north. Many hospitals in the state are still struggling with an influx of Covid-19 patients, which has overwhelmed ICUs in some regions. And overall statewide infections are still far higher now than they were early in the summer, when California averaged about 758 daily new cases as of July 1.

According to Bryan Bucklew, president and CEO of the Hospital Council of Northern & Central California, hospitals have been further strained by staffing shortages, primarily fueled by staff burnout and increased competition for nurses in other states.

"The numbers may be flattening, but the impact to the health care system is extremely challenging," he said. "We have a good handle on how to treat Covid, with monoclonal antibodies, vaccines. We just have a lot less staff. It's more of a workforce issue for us than a Covid issue."

In addition, the delta variant has been more difficult to control than earlier, less-infectious versions of the coronavirus, the Post reports, and a resurgence in cases in still a possibility.

According to Kirsten Bibbins-Domingo, an epidemiologist at the University of California, San Francisco, the delta variant is too contagious to completely wipe out, even in areas with high vaccination rates. In addition, a new school year, along with upcoming holidays and cold weather, will likely send many people indoors and could potentially lead to another surge in cases.

So far, California's public health measures have helped it control some of the virus's spread, but Schwartzberg warned that rolling back these restrictions too soon could reverse the progress the state has made.

"California has not been an exception to making this mistake," Schwartzberg said. "There's a pattern of surge, things get better, loosen up too soon. That stepwise fashion has been the pattern we’ve seen here and nationally."

"We need to learn from our past experience," he added. "I'm very concerned that we keep our foot on the brake for the rest of the fall and through January." (Karlamangla, New York Times, 9/16; Lin/Money, Los Angeles Times, 9/14; Hawkins/Dupree, Washington Post, 9/16)