The new rule requires everyone to wear masks in indoor public spaces regardless of their vaccination status, and took effect at 11:59 p.m.
The county reported 1,827 new cases of COVID-19 and 11 additional deaths on Saturday, as health officials attributed the recent spike to the presence of the more infectious Delta variant and the intermingling of unmasked individuals where vaccination status is unknown.
Saturday's daily test positivity rate was 3.7%. On July 4, it was near 1.5% and on June 15, test positivity was near 0.5%.
The number of people hospitalized in Los Angeles County due to the virus jumped from 462 on Friday to 507, while the number of those patients in intensive care remained at 103, according to state figures.
The latest figures lifted the cumulative total from throughout the pandemic to 1,266,227 cases and 24,579 fatalities, according to the Los Angeles County Department of Public Health.
Mask mandate: LA County orders face coverings indoors again as COVID cases spike
"Given the increased intermingling among unmasked people where vaccination status is unknown, the millions of people still unvaccinated, and the increased circulation of the highly transmissible Delta variant, we are seeing a rapid increase in COVID-19 infection,'' County Public Health Director Barbara Ferrer said. "The level of COVID-19 transmission we are currently experiencing is now leading to significant increases in serious illness and hospitalizations, and requires us to take immediate action to prevent erosion of our recovery efforts.
"And while vaccinations are by far the most powerful tool we have, we are nowhere near herd immunity. While we continue efforts to increase vaccination coverage and build confidence in the vaccines, the simplest and most effective public health measure to add back is to require that everyone wear a mask in all indoor public places and businesses. For those of us already vaccinated, we have been required for the last couple of months to continue to wear masks in many other public places including on all public transit, at all health care settings, schools and day care facilities. This was done in recognition that the vaccines, while extraordinarily effective, are not perfect and that we continue to have an obligation to reduce risk as much as possible.''
Not everyone at the county is on board with the new mandate.
Sheriff Alex Villanueva said Friday his deputies will not actively enforce the mask-wearing mandate, insisting his department is under-funded. He also said the requirement for vaccinated people to wear masks "is not backed by science and contradicts the U.S. Centers for Disease Control and Prevention guidelines.''
County Supervisor Kathryn Barger, the lone Republican on the five-member Board of Supervisors, also criticized the mandate for running afoul of federal and state rules on masking. She also said the mask mandate won't help the county's efforts "to stress the efficacy of the vaccines and compel unvaccinated residents to get vaccinated.''
"By deviating from the state, we create confusion and disagreement at the local level, which hinders public trust and takes away from our primary messaging which should be to encourage individuals to get vaccinated with urgency given the spread of the Delta variant,'' Barger said.
Fellow board members Hilda Solis, Janice Hahn and Sheila Kuehl have come out in favor of the mandate.
"The county has chosen a reasonable response given that virtually everyone agrees requiring proof of vaccination status before entering buildings is unrealistic,'' Kuehl said. "This keeps businesses open but makes it less likely unvaccinated people will just skip masks and put us all at risk. Until we can lower community transmission again and get more Angelenos vaccinated, we all need to pitch in and keep from providing breeding grounds for even more variants.''
Why is LA County re-imposing mask mandate? COVID positivity rate increased by 700% in one month
Hahn echoed that sentiment, saying on Twitter: "Right now, unvaccinated people are required to wear masks indoors -- but they aren't and they are spreading this virus to other unvaccinated people.''
Solis said Saturday that the new rule on face coverings was not tantamount to another lockdown.
"I want to emphasize that this indoor mask requirement does not stop us from enjoying all the great activities we have available through the county's re-opening,'' she said. "We can still go out and engage in indoor shopping, supporting our local restaurants through indoor dining, catching a great movie, and so much more.''
The masking mandate was announced Thursday by county Health Officer Dr. Muntu Davis. "We're not where we need to be for the millions at risk of infection here in Los Angeles County, and waiting to do something would be too late given what we're seeing now,'' Davis said.
Davis said the rate of virus spread in the county has officially risen from moderate to substantial, with infections five times more likely to occur among unvaccinated residents.
The county previously only recommended indoor mask-wearing by vaccinated people in an effort to slow the spread of the virus and protect unvaccinated residents. People who are unvaccinated have always been required to wear masks indoors, although enforcement was left up to individual business owners and was generally on the honor system.
The masking order will remain in place "until we see improvements'' in case transmission, he said.
Asked if the county might consider re-implementing other health restrictions -- such as capacity limits and physical distancing, Davis said, "Everything is on the table if things continue to get worse.''
Sheriff Villanueva won't enforce county's new mask order, claims 'not backed by science'
The mandate means customers will again be required to mask up when entering any indoor public establishment, including retail shops, grocery stores, restaurants and workplaces. Davis said indoor dining will remain open, but customers will have to remain masked while they are not eating or drinking.
Meanwhile, a gym in Sierra Madre is requiring members to provide proof of vaccination.
Beginning Monday, Sierra Health and Fitness is only allowing members who have been vaccinated. The owner said she's making the change to protect both members and workers.
"I need to do this because people trust me. We're in the healthcare business and we need to keep everyone safe," said owner Sandy Duvall. "We've never had a break out here, and I don't think we can move forward in the economy unless small businesses band together and do this."
The city of Long Beach, which has its own health department separate from the county, announced Thursday night it will align with the county and also require indoor mask wearing for all. In a statement, Long Beach officials said the city has seen a 288% increase in average daily cases over the past two weeks. The city's average daily rate of new cases has risen to 7.5 per 100,000 residents, up from an average of only one per 100,000 residents on June 15.
Pasadena, which also has its own health agency, has not aligned with the county and will continue only recommending indoor masking. But the city is monitoring "COVID case rates in Pasadena and are reviewing options for a mandate.''
City News Service contributed to this report.