A new COVID-19 variant — named lambda — has arrived in California.

The emerging lambda variant has been popping up in the news as it spreads rapidly throughout South America. In California, at least 152 cases have been reported, the first as early as September 2020, according to state public health officials.

Experts say lambda could be more infectious and resistant to vaccines than the original SARS-CoV-2 virus. But there is no evidence, at least so far, that it’s as infectious as the delta variant that now dominates California.

So do Californians need to worry about this new variant? Not just yet, infectious disease specialists say. Here’s what you need to know about lambda.

What is the lambda variant?

The lambda variant — also known as “C.37” — was first reported in Peru a year ago and it’s now spreading across South America, according to the World Health Organization. Researchers say its unique new gene deletions and mutations signal that lambda may be more infectious than the original “wild type” coronavirus and may be potentially resistant to current vaccines, although more studies are needed.

Because of those new genetic markers, the WHO in mid-June declared lambda a “variant of interest.” The U.S. Centers for Disease Control and Prevention has not yet done the same, in part because so few cases have been reported nationwide.

The delta variant dominating U.S. COVID-19 cases is considered a “variant of concern” by both WHO and CDC, in part because it’s much more infectious than the original virus.

Why am I hearing about lambda now?

Lambda sparked headlines this summer after the WHO noted its rapid spread in South American countries, including Peru, Ecuador, Argentina and Brazil. It’s since been detected in 29 countries, according to the WHO, including Germany, Spain, the United Kingdom and the United States.

While WHO considers lambda a “variant of interest,” the CDC and California’s public health agency have not followed suit.

In late July, Houston Methodist Hospital reported its first lambda case. Japan last week announced its first case, from a woman who arrived from Peru on July 20.

More recently, two highly publicized laboratory studies from Japan and Chile – both in preprint and not yet peer-reviewed – have suggested that lambda may be more infectious and less susceptible to current vaccines than the original coronavirus. The Japanese researchers suggested that WHO’s current “variant of interest” designation for lambda may underplay its potential threat.

Is lambda here in California? What about other states?

Yes and yes. Since September 2020, the lambda variant has accounted for 152 genetically sequenced COVID-19 cases in California, according to the state Department of Public Health. The first case was found in September, with another 10 in March, 88 in April, 43 in May, eight in June and, most recently, two cases in July.

The state agency declined to identify the counties where the cases occurred.

Commercial and government laboratories test for variants by sequencing the genome of the coronavirus that caused a particular COVID-19 case and looking for mutations and changes in the virus’ characteristic spike protein.

Still, not every COVID-19 case is genetically sequenced to determine whether it was caused by a variant, so the number of lambda-caused cases could be higher. Nationwide only about 15 of every 1,000 cases are sequenced.

At least 1,311 sequenced lambda cases have been reported in at least 40 states since the start of the pandemic, with 18 cases identified in the past four weeks, according to the public virus genetic sequence database GISAID. Just one-tenth of 1 percent of the cases that are genetically sequenced involve lambda, according to GISAID.

How does the lambda variant compare to other known variants?

Scientists believe lambda is less infectious than the delta variant but more infectious than the original “wild-type” virus – at least in laboratory tests.

But they don’t yet know how lambda’s different genetic profile will affect community transmission, severity of symptoms or vaccine resistance around the world. Some early clues are emerging.

The Chilean researchers tested lambda against antibodies from health care workers who received the Chinese-made Sinovac vaccine, finding that the vaccine failed to work as well as it did with the original virus.

Also, New York University researchers tested lambda against the vaccines authorized in the United States and found that the Johnson and Johnson one-dose vaccine was less effective against it and the delta variant compared to the Pfizer and Moderna two-dose vaccines.

Again, these are studies in test tubes that have not been peer reviewed, scientists caution.

Just because vaccines appear less effective when pitted against lambda in a test tube doesn’t mean they won’t protect against severe illness, said Dr. Peter Chin-Hong, a University of California, San Francisco infectious disease specialist. Nearly all hospitalizations and deaths in California and nationwide have occurred in unvaccinated people.

Do I need to worry?

Not for now, Chin-Hong said. Lambda has been around for months, yet it hasn’t gained a foothold in California and other states so that should be reassuring, he said.

So far the delta variant has definitively crowded out other variants nationwide. It now accounts for at least 86% of California’s sequenced COVID-19 cases and more than 94% of U.S. cases.

“Delta’s aggressive all over the world and lambda hasn’t really taken off,” Chin-Hong said. “At the end of the day, it’s survival of the fittest.”

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