Kat Schuster, Patch Staff

CALIFORNIA — Since the state reopened, many Californians have eased back into their social lives and liberated themselves from face masks. But the steady rise of the delta variant has posed increasingly more concern — especially for those who have not been vaccinated.

Delta is a mutation of alpha, another variant first discovered in the United Kingdom. Researchers are still working to determine whether the delta variant causes more severe disease, but there’s no doubt that it’s much more contagious.

“The strain is proving to be more transmissible and is expected to become more prevalent,” Los Angeles County public health Director Barbara Ferrer said in a statement Monday.

Here are five things to know about the troubling variant.

1. How widespread is the delta mutation?

The first known California cases were detected in April. Infections then made up just 1.8 percent of coronavirus cases. In May, that number crept up to 4.7 percent. As of Thursday, the variant was the third most common strain of the virus in the state — making up 14.5 percent of all cases.

Dr. Tomas Aragon, the state’s health director, said Tuesday that the variant “accounts for approximately 23 percent of cases sampled in California, and we anticipate this percentage will increase,” the San Francisco Chronicle reported.

Testing has also declined sharply in the Golden State in recent months. On April 17, 252,314 tests were reported within a 24-hour period. On Tuesday, the state reported just 113,653 tests in a day. That could mean that the true amount of cases is unknown.

As of Thursday, 372 cases had been reported in the state. In Los Angeles County, 123 cases had been identified, roughly double the number that was reported a week earlier. But since the county conducts limited sequential testing, which is required to identify the variant, the rising number means there are likely many more such infections, Ferrer said.

2. Will California consider another mask mandate?

For now, it seems that state officials are pushing for vaccinations instead of considering another mask mandate.

California will keep its mask guidance in alignment with the Centers for Disease Control and Prevention, Aragon said on Tuesday. But at least one county has sounded the alarm.

L.A. County public health officials diverged from federal and state guidance Monday by “strongly” recommending that everyone wear masks while indoors in public places because of the rapid spread of the delta mutation.

“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,” Ferrer said Monday.

Alternatively, in San Mateo County, a public health official told the San Francisco Chronicle that health officials there are more confident in its vaccination numbers.

“At the moment, given San Mateo County’s high vaccination rates, our health officer is not considering an indoor mask mandate,” Preston Merchant said. “We remain aligned with state directives and guidelines.”

As California reopened, the California Nurses Association issued a plea Monday to reconsider shedding masks in some situations the state deemed safe.

“Please, please just keep your masks on when you are indoors and in crowds,” said Zenei Triunfo-Cortez, a registered nurse and a president of the association. “It’s such a simple but effective way of preventing COVID-19. This pandemic is not over. We still have upwards of 10,000 new infections and hundreds of deaths per day. Not even half the U.S. population is fully vaccinated. And some of the new variants are highly contagious and incredibly troubling. Please keep on masking to protect yourselves and your families.”

Dr. John Swartzberg, an infectious disease expert and professor at the University of California, Berkeley, said earlier in June he’d rather err on the side of caution.

“I would put the needle more towards what CNA apparently is saying than what the governor is going to be saying,” Swartzberg said. “I’ve been fully vaccinated for a long time, but I’m not going to be going indoors without a mask on unless everybody I know who’s indoors with me is fully vaccinated.”

3. Are vaccinated Californians protected from this variant?

As far as researchers know so far, yes.

“There’s no reason to assume that these variants will completely escape an immune response from vaccinated people,” Dr. Timothy Brewer, an infectious disease expert and professor at the University of California, Los Angeles, told Patch in June. “For example, we know that variants that have similar mutations, such as the South Africa one, there are data to show that, particularly the mRNA vaccines, still provide protective immunity — albeit at a lower level — so I would assume they’ll similarly perform against the delta variant.”

So it’s still possible to become infected, but the chances of severe disease are low.

About 59 percent of Californians are fully vaccinated, according to state data. That leaves a large chunk of people unprotected from the more transmissible variant.

“The California Department of Public Health is closely monitoring the spread of COVID-19 and its variants across our state,” Aragon said Tuesday, according to the San Francisco Chronicle. He added: “The most important thing we can do to stop the spread of COVID-19 is ensure everyone who is eligible gets vaccinated.”

4. The delta variant is a ‘variant of concern.’ What does that mean?

The CDC labeled the delta variant a “variant of concern” in June. The variant is reportedly twice as likely to send an unvaccinated infected person to the hospital as the alpha variant first detected in the United Kingdom, according to a Monday report published in The Lancet.

The nation’s top infectious disease expert and White House chief medical advisor, Dr. Anthony Fauci, said last week that the delta variant accounted for 20 percent of newly diagnosed cases in the U.S., CNBC reported.

“It just exploded in the U.K. It went from a minor variant to now more than 90 percent of the isolates in the U.K.,” Fauci told NBC.

He said the variant has a doubling time of two weeks. At a White House briefing last week, Fauci also called the variant the greatest threat to the nation’s efforts to end the pandemic.