The recommendation, which officials say is a precautionary measure, is a shift from current guidance, which allows fully vaccinated people to go maskless in most settings.
"Public Health strongly recommends people wear masks indoors in settings such as grocery or retail stores; theaters and family entertainment centers, and workplaces when you don't know everyone's vaccination status," L.A. County Department of Public Health said in a statement.
"Until we better understand how and to who the Delta variant is spreading, everyone should focus on maximum protection with minimum interruption to routine as all businesses operate without other restrictions, like physical distancing and capacity limits," the statement added.
The Delta variant of COVID-19 originated in India, and is blamed for rampant infections in that country and outbreaks in the United Kingdom and beyond. Federal health authorities estimate that 20% of all new COVID infections in the country are now due to the Delta variant, up from 10% a week ago.
Delta variant of COVID-19 a rising concern in Los Angeles County
"We adhere our orders to the county orders," Los Angeles Mayor Eric Garcetti said Tuesday morning. "So we say: Indoors, in those work settings, in those retail settings, we suggest that you should. This is not a mandate at this point. But especially for those who are unvaccinated: Protect yourself.
Garcetti noted that the best way to protect oneself is "not a mask -- it's the vaccination."
The Delta variant is considered to be far more contagious than previous mutations of the COVID-19 virus, and potentially capable of making patients more severely ill. Health officials have said people who are fully vaccinated are protected against the variant.
"While COVID-19 vaccine provides very effective protection preventing hospitalizations and deaths against the Delta variant, the strain is proving to be more transmissible and is expected to become more prevalent,'' L.A. County Public Health Director Barbara Ferrer said in a statement. "Mask wearing remains an effective tool for reducing transmission, especially indoors where the virus may be easily spread through inhalation of aerosols emitted by an infected person."
Last week, Ferrer said a total of 123 cases of the Delta variant had been identified in the county, roughly double the number from a week earlier. But since the county conducts very limited sequential testing required to identify the variant, she said the rising number means there are likely many more such infections in the community.
Ferrer stressed the level of protection offered by the COVID vaccines, releasing statistics showing that between Dec. 7 and June 7, 99.6% of all new COVID infections in the county involved people who were not vaccinated. Of the people who were hospitalized due to the virus in that time period, 98.7% were unvaccinated. And among those who died, 99.8% were unvaccinated.
City News Service contributed to this report.