Starting on Sunday, indoor masking is back in Los Angeles for everyone — even for the fully vaccinated.

The announcement this week came amid a concerning rise in COVID-19 cases, and exactly one month after California dropped its statewide mask mandate for vaccinated people.

Previously, public health officials recommended indoor mask-wearing only among the unvaccinated, but the rise of the more easily spread Delta variant has complicated reopening efforts across the country — creating what the Director of the CDC recently called a “pandemic of the unvaccinated.”

In L.A., new case numbers have topped 1,000 for at least seven days straight, and just this week saw more than 1,500 new infections, the highest number since early March. The situation has prompted Sacramento and Fresno Counties to strongly urge people to wear masks indoors without mandating it.

The shifting mask requirements have forced local businesses, which have been struggling to recover from COVID-19 lockdowns, to adapt quickly.

“The mask mandate is not as critical as just closing again and locking down,” Carolina Martinez, CEO of CAMEO- California’s statewide micro-business network and leading voice for businesses with one to four employees, told Yahoo Finance in an interview.

The organization “has been working with small businesses to try to help them adjust to how they could continue operations, respecting safety and regulations. It's definitely a challenge,” Martinez added.

Delta variant upends reopening strategy

Data from the CDC shows high levels of coronavirus transmission in numerous states, including Missouri, Mississippi, Florida, Nevada and Utah.

In Los Angeles, cases are rising among the unvaccinated, estimated to be around 4 million residents. Currently, 69% of L.A.’s population over 16 have received at least one dose of the vaccine, and 61% are fully vaccinated.

Other California counties and other states are also grappling with a spike in coronavirus cases, led by the Delta variant that's predominantly affecting the unvaccinated. In June, the strain comprised 43% of all California’s confirmed cases of COVID-19.

However, vaccine status verification is difficult for a number of reasons, so some places require frontline employees to wear masks. Recently, With Love Market and Cafe founder and operator Andrew McDowell told his staff they will be wearing their masks “indefinitely."

During the worst days of COVID-19, mask mandates became a cultural and political flashpoint between supporters and opponents of public health policy, especially in epicenters like California and New York.

"The focus for us really is, what are the things we need to put in place to make sure our staff are safe, and safe staff [is] going to mean safer customer [s]," McDowell told Yahoo Finance Live in an interview earlier this month.

“If we keep changing and yoyo-ing, it's going to be a challenge for us,” he added. “We just have to do the best that we can, to be safe and consistent, and just wait this out.”

There continues to be a push to get people vaccinated, with data showing Black and Latino populations are getting shots at a lower rate than others.

Dani Romero is a reporter for Yahoo Finance. Follow her on Twitter: @daniromerotv

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