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Starting at 11:59 p.m. Saturday night, Los Angeles County residents will again be required to wear masks in all indoor public settings, regardless of their vaccination status.

The mask mandate comes amid a spike in coronavirus cases and hospitalizations in the region. Health officials say the county has been seeing “alarming trends of increased community spread” after reporting more than 1,000 daily new cases for several consecutive days.

“We have all seen COVID-19 spread very fast in just a small amount time.  The alarming increases in cases, positivity rates and the increase in hospitalizations signals immediate action must be taken to slow the spread of COVID-19,” L.A. County Health Officer Dr. Muntu Davis stated in a news release Friday.

A month after the delta variant became the most dominant in the region, daily case increases have reached levels not seen since March.

Cases are the highest and increasing the fastest among adults age 18 to 49 years old, according to the county public health data.  Of the new cases reported Friday, 71% were among adults in that age group.

Officials say that about 99% of the people getting sick are unvaccinated. This mirrors trends seen nationwide, as more than 97% of COVID-19 patients entering hospitals across the country are unvaccinated, according to Dr. Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention.

According to the county’s vaccination data, just over 60% of L.A. County residents are fully vaccinated, and nearly 70% have gotten at least one shot. But in the nation’s most populous county, that still leaves millions vulnerable.

“Without physical distancing and capacity limits during a time of substantial community spread, masking by everyone indoors is a simple and effective action we all can take to lower risk of transmission while limiting disruption to normal business capacity and operations,” Davis said.

Long Beach, which has its own public health department, announced on Friday that the city will be aligning with L.A. County in requiring masking indoors, regardless of vaccination status.

The other city in the county with an independent public health department, Pasadena, already recommends that everyone — including the fully vaccinated — wear masks in indoor public settings.

Meanwhile, L.A. County’s latest mask mandate puts the region’s public health department at odds with both the state’s public health department and the U.S. Centers for Disease Control and Prevention — both of which say that vaccinated people do not need to wear masks in most indoor places.