Nurse Jessica Lipscomb gives Miguel Castro, 13, of Brentwood, the Pfizer COVID-19 vaccine in the Antioch Middle School gym in Antioch, Calif., May 19, 2021. In partnership with Kaiser Permanente and the Contra Costa Office of Education, the Contra Costa Health Services have started school-based COVID-19 vaccination clinics. While coronavirus cases remain low in California, the nation’s most populous state has recently seen hospitalizations creep back up slightly. (Doug Duran/Bay Area News Group via AP)

LOS ANGELES (AP) โ€” California broadly reopened its economy barely two weeks ago and since then an especially contagious coronavirus variant has spread among the unvaccinated, a development that has health officials on edge and already has prompted Los Angeles County to strongly recommend everyone resume wearing masks inside.

The nationโ€™s most populous state is averaging close to 1,000 additional cases reported daily, an increase of about 17% in the last 14 days. Officials expected an increase when capacity limits were lifted for businesses and most mask restrictions and social distancing requirements were eliminated for vaccinated people.

But public health officials raised concern this week with the more transmissible delta variant spreading among the unvaccinated, who comprise the vast majority of new infections. LA County, where a quarter of the stateโ€™s nearly 40 million people live, recommended Monday that vaccinated residents resume wearing face coverings indoors after detecting that about half of all cases were the delta variant.

โ€œThe new wrinkle in this is really this new variant. It just sort of rips very quickly through people who are susceptible to being infected, which overwhelmingly is people who are not vaccinated,โ€ said Kirsten Bibbins-Domingo, professor of epidemiology at the University of California, San Francisco. โ€œWe just opened up two weeks ago, everything was hunky dory.โ€

Gov. Gavin Newsom lifted a series of pandemic-related restrictions on June 15 after a final push to get more people vaccinated. Everyone 12 and older is eligible for shots and among that population 59% is fully vaccinated and another 10% has received a first dose.

In Contra Costa County, where 72% of eligible residents are fully vaccinated, officials recently began publishing virus case rates by vaccination status. Since the county has a high inoculation rate, the number of new coronavirus cases is generally low but unvaccinated residents remain at risk, said Dr. Chris Farnitano, the countyโ€™s health officer.

For example, the seven-day average of new virus cases per 100,000 people in the county was recently 7.0 for those who are unvaccinated, and 0.4 for those who are vaccinated.

โ€œThe overall numbers donโ€™t look that concerning, but we know that thereโ€™s this population that hasnโ€™t been vaccinated that still is at very high risk, and those overall numbers can give a false sense of security thinking COVID is still under control where itโ€™s still spreading quite rapidly among the unvaccinated population,โ€ Farnitano said.

In Los Angeles, a mix of masked and unmasked people walked around Echo Park Lake on Wednesday. G. Williams, who waited for a bus nearby, wore a black cloth mask over a blue surgical one โ€” something she expects sheโ€™ll do for years to come.

The 69-year-old isnโ€™t vaccinated, saying she still has concerns about possible long-term side effects. She supports her countyโ€™s latest recommendation and said she doesnโ€™t understand why people wouldnโ€™t wear a mask to protect others.

โ€œTo me, my mask is as important as any article of clothing,โ€ she said.

At Raven Things Collected, an LA gift shop selling crystals, tarot cards and jewelry, a table full of merchandise has been pulled in front of the counter to keep everyone distanced.

Employee Yesenia Rego said she feels protected because sheโ€™s vaccinated and distanced from customers. Most people wear masks when they come in anyway, she said, adding those who donโ€™t rarely ask if they should.

โ€œThey donโ€™t even care anymore,โ€ said Rego, 23, who wore a green cloth mask.

Vaccination rates vary widely across California. A San Francisco ZIP code reports more than 95% of those eligible are fully inoculated, while one in rural Modoc County has a 37% rate, according to state data.

Health officials said areas with low vaccination rates are especially at risk as the delta variant, first reported in India, spreads across the United States. The variant โ€” which accounts for a fifth of new U.S. infections โ€” was found in 15% of specimens sequenced in California in June, up from 5% in May.

In Orange County, the variant accounts for 45% of sequenced cases in the most recent week, said Dr. Regina Chinsio-Kwong, the countyโ€™s deputy health officer. Contact tracers reaching out to those infected with the virus find 95% are unvaccinated, and the few who are vaccinated report minor symptoms and arenโ€™t hospitalized, she said.

โ€œBecause weโ€™re starting to see these highly transmissible strains, it is only a matter of time for us to be exposed again,โ€ she said. โ€œSo the question is how severe is the illness going to be when you actually get COVID.โ€

Public health officials said they hope measures like the one taken by Contra Costa County might help encourage more people to get the shots.

โ€œItโ€™s a demonstration in the real world, outside of the clinical trials, of the power of the vaccine,โ€ said Andrew Noymer, a public health professor at University of California, Irvine. โ€œCOVID is going to seek out unvaccinated populations. The virus has a way of just sort of bouncing around until it finds a host it can infect, and those will be unvaccinated people.โ€