A coronavirus variant identified in California seems more infectious and deadly, a study found, with cases thought to be doubling every 18 days - but the scale of the threat is unclear

• A study suggests a coronavirus variant first found in California is more contagious and deadly.
• The early study, first reported by Science, hasn't been formally scrutinized in a peer review.
• Some experts say more data is needed before the strain is considered especially dangerous.

An early study has suggested that a coronavirus variant first found in California is more infectious than the original virus strain, more likely to be associated with severe illness, and partially resistant to antibodies.

"The devil is already here," Charles Chiu, an infectious-disease physician and sequencing expert at University of California at San Franciso who led the study, told the Los Angeles Times. "I wish it were different. But the science is the science."

Other experts say more data is needed before conclusions are drawn about the variant.

The variant consists of two slightly different mutated forms of the virus, called B.1.427 and B.1.429. It is also called CAL.20C, using another naming system. It was first found in California in July and has now been detected across the US and elsewhere including Australia, Denmark, Mexico, and Taiwan, according to GISAID.

The study authors said the variant "should likely be designated a variant of concern warranting urgent follow-up investigation," Science reported Tuesday. A variant of concern is a variant that has been risk-assessed by experts for concerning features, such as being highly infectious, making people sicker, or escaping the immune response produced by vaccines.

The study has not been posted online or formally scrutinized by experts in a peer review.

Eric Topol, the founder and director of the Scripps Research Translational Institute, said on Twitter that there was "a problem" with labeling the variant "dangerous" without the study being published and while COVID-19 cases, hospitalizations, and deaths were falling despite the variant being widespread.

"If I were a reviewer, I would want to see more data from more infected people to substantiate this very provocative claim," David O'Connor, a viral-sequencing expert at the University of Wisconsin at Madison, told Science.

Chiu and his colleagues examined 2,172 virus samples collected from 44 of California's 58 counties from September 1 to January 29. At the start of September, they found no cases caused by B.1.427 or B.1.429. By late January, the variant accounted for more than half of cases sequenced. From the data, Chiu and his colleagues estimated that the number of cases caused by the variant was doubling every 18 days, The New York Times reported.

Bruce Walker, an immunologist and founding director of the Ragon Institute in Boston, told the Los Angeles Times that it was hard "to disentangle" all the factors that contribute to spread, including travel, holiday gatherings, and restaurant dining.

"I'm increasingly convinced that this one is transmitting more than others locally," William Hanage, an epidemiologist at the Harvard TH Chan School of Public Health, told The New York Times. "But there's not evidence to suggest that it's in the same ballpark" as B.1.1.7, the variant first identified in the UK that many project will become the dominant strain in the US.

Variant has a key mutation

The study authors identified some possibilities as to why the B.1.427/B.1.429 variant could be more infectious. First, they found that there was twice the amount of virus on nasal swabs from those who were infected with B.1.427/B.1.429 as there was on those who weren't. This could mean people with the variant carry more virus particles, which makes them more likely to pass the virus to others.

Second, the variant in California has a mutation called L452R in its spike protein - the part of the virus used to infect cells. The authors engineered a coronavirus with the L452R mutation and found it was able to infect human lung tissue at least 40% more readily than other variants and was three times as infectious. L452R hasn't been seen in the existing variants of concern.

Third, the scientists found that the antibodies produced by the human body to fight infection worked only half as well against B.1.427/B.1.429 as they did with the original coronavirus variant. The effect was less pronounced than for the variant first discovered in South Africa, which was found to reduce the antibodies' efficacy to one-sixth of their usual levels.

If antibodies work less well, it could mean there's increased risk of reinfection, and vaccines could be less effective. Another preprint study, however, has found that the variant first found in California produced a similar antibody response to the original coronavirus.

Ciui and his team also said the variant could be more deadly.

The team studied 324 medical records from UCSF clinics and its medical center and found those carrying the variant were 4.8 times as likely to be admitted to intensive care and more than 11 times as likely to die compared with those infected with other variants, Science reported.

Ciui's team said it adjusted for differences in age, gender, and ethnicity. The sample was small, though, and it was not possible to tell whether more people died because of the B.1.427 /B.1.429 variant itself, or whether overwhelmed hospitals and possible suboptimal care as a result contributed to their deaths, the authors said.