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Two potentially more infectious variants of the coronavirus, one first identified in South Africa and the other in Brazil, have surfaced in Los Angeles County for the first time, public health officials announced Wednesday.

The mutated version of the virus first identified in South Africa, known as the B.1.351 variant, was found in one case last week. Meanwhile, another variant of concern first detected in Brazil, known as the P.1 variant, was found in three cases.

“Although these are the first reported cases of the South Africa and Brazil variant in L.A. County, it is likely there are additional undetected and undiagnosed cases,” Public Health Director Barbara Ferrer said in a virtual briefing Wednesday.

That’s because “very few” of the county’s coronavirus specimens undergo genomic sequencing to determine the variant type, Ferrer said. 

“The CDC has classified the South Africa and Brazil variants as variants of concern, because they’re potentially associated with increased transmissibility and reduced,” Ferrer said. “The identification of these variants highlights the need for LA County residents to continue to do everything we can take measures to protect ourselves and others.”

Also concerning, Ferrer noted, is that the majority of the county’s COVID-19 positive samples genomically analyzed over the past week turned out to be variants of concern. 

Of the roughly 70 samples reanalyzed in L.A. County last week, 64% of the specimens turned up to be the variant first identified in the United Kingdom, and 20% “were the California variant of concern,” Ferrer said. 

She said the “significant increase” in the positive cases with the variant from the U.K. mirrors trends seen across the country, “as this variant is now thought to be circulating more widely.”

“As a reminder, while the specimen sequence are not randomly selected, increases in the percent of variants identified most probably correlates with increased circulation of the known variance,” Ferrer said.

Other coronavirus variants detected this past week include three cases of the variant first identified in New York, she added.

“With the majority of variants identified in LA County this week being variants of concern, it’s more important than ever that we took a lot precautions, particularly during our reopening,” Ferrer said. 

The discovery of the variants from Brazil and South Africa in L.A. County comes just two days after the state announced its first case of an emerging “double mutant” variant that reportedly originated in India. However, it is unclear at this time if this particular mutant is more contagious or resistant to the existing vaccines.

Despite the increase in coronavirus variants among COVID-19 positive cases in the region, Gov. Gavin Newsom announced Tuesday that the state plans to drop most of its pandemic restrictions on June 15 so long as infection and vaccination numbers continue to move in the right direction.

That may become a challenge as some key pandemic indicators have plateaued in Los Angeles and Orange counties this past week.

L.A. County has so far avoided a spike in new coronavirus cases that have plagued other parts of the country — a result of vaccinations and efforts to change behaviors to limit spread, Ferrer said.

But for the second week, the region’s adjusted case rate — a key metric in determining counties can move tiers — remained at 3.1 new cases per 100,000 after weeks of steep, consistent declines.

“This reflects that while our case numbers remain relatively low, we are not continuing to see the significant decline in the number of new cases,” Ferrer said. “Cases are not going down anymore. We’ve kind of plateaued.”

On Wednesday, L.A. County reported 479 new coronavirus cases and 53 additional deaths related to COVID-19, bringing the region’s totals to 1,223,174 cases and 23,340 deaths.