As COVID-19 infections rise due to the extremely contagious Delta strain, San Francisco and six other Bay Area counties said Monday that they will reinstate a mask requirement for all indoor public places.

The new law takes effect on Tuesday in San Francisco, Alameda, Contra Costa, Marin, San Mateo, Santa Clara, and Sonoma counties, as well as the city of Berkeley, and applies to everyone, regardless of immunization status.

Bay Area health officers also urged that people assemble outside if they have the possibility during a news conference announcing the new orders.

“It's unfortunate that we have to do this at this stage of the outbreak. “None of us wanted to be here,” said Dr. George Han, Santa Clara County's deputy health officer. “However, the virus has evolved.”

According to Sundari Mase, the interim health officer for Sonoma County, north of San Francisco, the Delta variation accounts for 95 percent of new coronavirus cases in the area. “Right now, we're up against a much more aggressive and contagious opponent,” she explained.

Although unvaccinated people account for the great majority of new cases and hospitalizations, the Bay Area mandate affects everyone due to an increase in the number of vaccinated people testing positive and evidence that vaccinated people can transmit the virus.

According to Mase and other health experts, the very small number of vaccinated people who are currently hospitalized is mostly made up of the elderly or those with serious underlying health concerns.

California this week suggested that everyone wear masks indoors, regardless of vaccination status, in accordance with CDC recommendations, but officials stopped short of requiring it.

Indoor mask laws are already in place in the counties of Los Angeles, Yolo, and Sacramento. Louisiana, which has one of the lowest immunization rates in the country, restored a mask mandate on Monday, taking it a step further by including schools and universities.

At the commencement of the pandemic in March 2020, health officials in the San Francisco Bay Area were the first in the country to announce a shutdown.

With more than 60% of individuals fully vaccinated, the region tops the state in vaccination rates. Marin County, located north of San Francisco, has the highest vaccination rate, with over 73 percent of its population having received the vaccine.

Since the state fully reopened its economy on June 15 and removed indoor and outdoor capacity constraints as well as social barriers, the number of viral cases has steadily increased.

Health officials in the Bay Area said they took action on Monday because of alarmingly high hospitalization rates, and that they will consider removing the new limits after those rates drop.

“We are alarmed at the rate at which COVID patients are filling our community hospital beds,” said Chris Farnitano, Contra Costa County's health officer, who noted that the number of hospitalized COVID patients has doubled in the last ten days and climbed by more than 400% in July.

He urged unvaccinated persons to get immunizations and warned that indoor gatherings pose the greatest danger of viral propagation. “I would strongly advise against higher-risk indoor activities like eating in an indoor restaurant, exercising in a gym, or going to a movie theater if you are unvaccinated,” Farnitano said.

Indoor restaurant dining will be permitted, but guests will be required to wear masks when not eating or drinking. Face coverings are required in other public places, such as gyms and movie theaters, though enforcement varies by location.

Businesses in Santa Clara County would be obligated to enforce the mask mandate, and citizens will be able to file complaints on the health department's website, according to Han.

Businesses in Berkeley, which is in Alameda County but has its own public health department, will be obliged to post signs saying that masks are necessary indoors under the new order, according to Lisa Hernandez, the city's health officer.

San Francisco's new directive will not be enforced, instead of relying on people's willingness to "follow the science and the data," according to Naveena Bobba, the city's deputy director of health.

COVID-19 immunizations were made required for an estimated 239,000 Kaiser Permanente employees and clinicians on Monday, joining other U.S. corporations and public health departments.

Nearly 78 percent of the company's employees and more than 95 percent of its physicians are completely vaccinated, according to the Oakland-based health care and health plan provider.