Highly infectious Delta variant spreading rapidly, now California’s dominant coronavirus strain

Electron microscope image shows SARS-CoV-2
This transmission electron microscope image shows SARS-CoV-2, the coronavirus that causes COVID-19.
(National Institute of Allergy and Infectious Diseases Rocky Mountain Laboratories)

The highly infectious Delta has become California’s most identified variant of the coronavirus, a troubling development that underscores its danger to unvaccinated populations.

New data released by the California Department of Public Health say 35.6% of coronavirus variants analyzed in June have been identified as Delta, which was first identified in India. That’s a dramatic increase from May, when Delta accounted for just 5.6% of analyzed coronavirus cases in California and was the state’s fourth most identified variant.

Delta is now more widespread than the previous dominant strain, Alpha, which was first identified in the United Kingdom and accounted for 34.3% of analyzed coronavirus cases in June. Alpha was the state’s most dominant strain in April and May, outpacing the California variant, now known as Epsilon, which currently occurs in less than 2% of analyzed cases.


The rapid rise of Delta is prompting some public health officials to issue new warnings, urging more caution at a time when vaccinated people are putting away masks and getting back to normal life. Although those who have been fully vaccinated are believed to have high levels of protection, there is growing concern about the virus spreading among people who have not been inoculated.

Coronavirus cases and hospitalizations have been ticking up in Los Angeles County, where some 4 million people, including 1.3 million who are not yet eligible, have not had a single dose of vaccine.

Delta might be twice as contagious as the initial variants of the coronavirus that spread rapidly around the globe last year.

“The rapid increase in the Delta variant suggests that this strain is more easily transmitted between people than other strains circulating in California,” the state Department of Public Health said in a statement to the Los Angeles Times.

“Nevertheless, there is evidence that vaccines available in the U.S. are effective against the Delta variant,” state officials added.

Delta is also spreading rapidly nationwide. The director of the U.S. Centers for Disease Control and Prevention, Dr. Rochelle Walensky, said recent data show that 25% of analyzed coronavirus cases nationwide are of the Delta variant. In some areas of the country, nearly half of analyzed cases are Delta.

By contrast, from May 9 to May 22, Delta made up less than 3% of analyzed coronavirus samples nationwide.

There are reports of rapidly increasing Delta cases confirmed in Los Angeles County too. The county started seeing upticks in early April. In May, the county had fewer than 20 identified Delta cases a week, but by June, there were 60 to 80.

For the week that ended June 19, Delta made up nearly 50% of all cases analyzed in L.A. County; four weeks earlier, it accounted for less than 5%.


Delta has been identified in 245 coronavirus cases so far in L.A. County, with early clusters identified in Palmdale and Lancaster. Fourteen cases of Delta occurred among residents of a single household.

The increase in the proportion of identified Delta cases comes as COVID-19 hospitalizations have started to rise again in L.A. County and across the state.

Lab tests and real-world experience offer reassuring evidence that COVID-19 vaccines offer a high level of protection against the Delta variant.

July 2, 2021

The number of Californians hospitalized for COVID-19 fell to 915 on June 12 — the lowest it has been since the state began tracking cases. By Saturday, there were 1,097 COVID-19 patients in hospitals statewide, a 20% increase.

COVID-19 hospitalizations in L.A. County hit a record low of 212 on June 12. But on Saturday, there were 284 hospitalized patients — a 34% increase, though far below the peak of 8,098 during the worst days of the pandemic.

State officials say they don’t expect California’s hospitals to once again be overwhelmed with COVID-19 patients — there are simply too many vaccinated people around to imagine such a scenario.

But officials noted that it remains crucial that more Californians get vaccinated.

“We know our hospitalizations are creeping up — and most of the patients are unvaccinated. We also know the science is clear — getting vaccinated protects you AND those around you. Get vaccinated,” Gov. Gavin Newsom tweeted.

His comments echoed those by Dr. Anthony Fauci, the U.S. government’s top infectious-diseases expert. He pointed to recent studies showing that the Pfizer-BioNTech vaccine was 88% effective against symptomatic disease from the Delta variant and 96% effective against hospitalization after two doses were administered. The AstraZeneca vaccine, which is not approved for use in the U.S. but uses similar technology to the Johnson & Johnson vaccine, was found to be 92% effective against hospitalization.


“The best way to protect yourself against the virus and its variants is to be fully vaccinated. It works,” Fauci said.

In Los Angeles County, a sudden rise in coronavirus cases and hospitalizations has put a damper on the holiday spirit.

July 3, 2021

Some officials, however, have said the science isn’t settled on whether some vaccinated people could be at higher risk of contracting the Delta variant and passing it to other people, while not getting severely sick themselves.

That was the reasoning behind the L.A. County Department of Public Health’s latest recommendation that even fully vaccinated people return to wearing masks in indoor public settings until more definitive information emerges about Delta.

L.A. County officials expressed worry over a recent doubling of new coronavirus cases of all variants. From June 25 to July 1, the county reported about 2,600 new cases; the previous week’s sum was about 1,100.

“Whenever you see a doubling of cases over a very short time, we all need to pay attention to that, and we all need to think about what else we could be doing that may help us get back to reducing the spread,” said L.A. County Public Health Director Barbara Ferrer.


She too noted that fully vaccinated people are highly protected against serious illness and death from COVID-19, including from the Delta variant. But, she added, “the big unknown is: Can you become infected — have mild illness — and go ahead and spread that infection to others?”

Until more information comes out about that, Ferrer requested that L.A. County residents mask up in indoor settings where vaccination statuses may be unknown. “If mask wearing indoors provides that extra layer of protection, I think it’s worth it, while we get more questions answered about the variant, and we get more people vaccinated.”

Others who have suggested that even vaccinated people wear masks include Illinois Gov. J.B. Pritzker, the government of Israel, the World Health Organization and health officials in the St. Louis area.

The Times interviewed 10 Southern Californians about what the Fourth of July means to them, in the wake of the hell year that was 2020.

July 4, 2021

The federal Centers for Disease Control and Prevention has continued to say that fully vaccinated people do not need to wear masks because of the high levels of protection offered by the vaccines authorized in the U.S.

“If you are vaccinated, you have a high degree of protection, so you need not wear a mask — either indoor or outdoor,” Fauci said.

He added that local authorities are free to make their own recommendations or requirements based on regional conditions.


California officials and local health agencies throughout the state have continued to align with the CDC guidance on masking recommendations.