Los Angeles County is experiencing a rise in new coronavirus infections, a concerning trend given the continued circulation of the highly transmissible Delta variant, officials say.
As of Thursday, 245 Delta cases had been confirmed countywide — double the number last week.
Officials say the variant, which may be twice as transmissible as the conventional coronavirus strain, has the potential to spread rapidly among unvaccinated segments of the population.
And though L.A. County's overall coronavirus metrics remain relatively low, any increases in transmission have the potential to spur more infections, illness and death in a region already familiar with the suffering COVID-19 can cause.
"The rising proportion of Delta among sequenced variants of concern is consistent with what other parts of the U.S. are seeing, and for certain represents increased circulation of the variant," Public Health Director Barbara Ferrer said. "Given that 4 million residents in L.A. County are not yet vaccinated, the risk of increased spread is very real."
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L.A. County averaged about 298 new coronavirus cases a day over the seven-day period that ended Wednesday, an 85% increase from the daily case rate for the seven-day period that ended June 24.
The daily case rate is still more than 98% lower than during the peak of the pandemic, when L.A. County was averaging more than 15,000 new cases a day.
COVID-19 hospitalizations have started to tick upward in L.A. County too. As of Wednesday, there were 280 patients with COVID-19 in hospitals, up from 213 on June 19.
The latest figure is 97% lower than during the peak of the pandemic.
Over the last week, California has reported an average of 942 new coronavirus cases per day — up about 7% from two weeks ago, The Times’ data show.
The increases seen recently, combined with the presence of Delta, are behind L.A. County's recent recommendation that even vaccinated people should wear masks indoors. Though available data indicate those who are inoculated enjoy strong protection against the various coronavirus variants, there are concerns that Delta could spread in populations that are not vaccinated, or have yet to complete their vaccine regimen.
Only about 50% of Californians, and a similar share of Angelenos, are fully vaccinated.
In a county the size of Los Angeles, that still leaves millions of people exposed to potential future outbreaks.
“Given that we have large numbers of unvaccinated people in Los Angeles County — 4 million in total, including 1.3 million children not yet eligible to be vaccinated — another wave could become a very real possibility,” Ferrer said Thursday.
On June 15, California’s reopening day, Los Angeles County recorded 210 new coronavirus cases, and the proportion of conducted tests coming back positive was hovering around 0.5%.
Both those metrics had doubled by Wednesday, with the county reporting 422 new cases and a test positivity rate of 1.2%.
The seven-day statewide positivity rate also in effect doubled over that same period, according to the California Department of Public Health.
Ferrer has previously said one factor that could be inflating the positivity rate is that schools have let out for the summer, which significantly shrank the number of people undergoing routine surveillance testing.
That means the testing pool is not only shallower, but also probably filled more predominantly with residents who are symptomatic or have been exposed to someone with COVID-19.
Dr. Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention, said an estimated 25% of new coronavirus cases sequenced nationwide are now of the Delta variant, and she expects it eventually will become the dominant strain in the nation.
“As the Delta variant continues to spread across the country, we expect to see increased transmission in these communities unless we can vaccinate more people now,” she said.
California officials repeated that view.
“The risk for COVID-19 exposure and infection will remain in California until we reach community immunity with vaccinations,” said Dr. Tomás Aragón, director of the California Department of Public Health and the state’s public health officer. “COVID-19 vaccines provide excellent protection from serious disease, even for the Delta variant.”
Circulation of the variant has increased rapidly since it appeared in California.
Delta made up just 1.8% of coronavirus cases analyzed in April, state public health data show.
That proportion jumped to 4.7% in May. As of last week, the variant made up 14.5% of specimens sequenced during June.
On Tuesday, Aragón said the variant accounted for about 23% of sampled cases, “and we anticipate this percentage will increase.”
“We have enough risk and enough unvaccinated people for Delta to pose a threat to our recovery,” Ferrer told reporters Thursday. “And masking up now could help prevent a resurgence in transmission.”
This story originally appeared in Los Angeles Times.