California coronavirus variant possibly more infectious, might cause more serious illness, S.F. studies show – San Francisco Chronicle

A California-bred variant that has spread widely across much of the state since the start of the year appears to be more infectious than other versions of the coronavirus, and may also cause more serious illness and be somewhat resistant to the body’s immune response, according to two studies released Monday.

The studies, out of UCSF and the Chan Zuckerberg Biohub, are the first to demonstrate that the so-called California variant spreads more easily than others and has other worrisome traits. Scientists had suspected the variant was more infectious based on how quickly it exploded in parts of the state, and because it had been tied to several large outbreaks, but they lacked firm evidence until now.

Scientists at the Chan Zuckerberg Biohub and UCSF looked at positive test results in the Mission District and found that about 35% of household members became infected when one case of the California variant was brought into the home; the attack rate for other variants was about 26%. The variant has rapidly become more common in the Mission, too. Genomic sequencing found the variant in more than half of all samples in January, up from 16% in November.

Separately, a study by Dr. Charles Chiu at UCSF also found evidence that the variant is more infectious. In addition, his team found that people infected with the variant were more likely to end up in intensive care or die. And lab tests showed the variant was less responsive to antibodies produced by people who had previously been infected. It’s not clear from the results whether the variant is less responsive to vaccines.

It “should likely be designated a variant of concern warranting urgent follow-up investigation,” Chiu and a team of authors wrote in a paper on the study. Both studies have not yet been published.

“We don’t want to be alarmist. It’s not as aggressive as the U.K. variant,” said Joe DeRisi, co-president of the Biohub, of the results of the Mission District study. The variant from the United Kingdom, known as B.1.117, is thought to be roughly 50% more infectious than the original virus out of China. “But it highlights the need to examine this strain more carefully and do more studies on it. We need to be aware that it’s in the community and spreading fast.”

Coronavirus variants have become a growing concern in the pandemic, as mutated versions of the virus emerge around the world that are more infectious, cause more serious illness or are partly resistant to vaccines. Public health officials are racing to vaccinate large swaths of the country in part to drive down cases and prevent the virus from mutating further.

Infectious disease experts first became concerned about the California variant in January, when two teams of scientists — one at UCSF and one in Los Angeles — identified it independently as spreading fast in a few communities, including some in the Bay Area. The variant was found to be the source of a large outbreak at Kaiser Permanente in San Jose in which more than 90 people were infected.

There’s been some confusion over what to call the California variant, which may be two separate but very similar variants that share the same key mutations. The California Department of Public Health refers to them as B.1.429 and B.1.427, but both variants also are called CAL.20C or sometimes referred to by a single mutation, L452R.

That mutation is key to the California variant. It’s located on the spike protein — a spot on the virus where it attaches to human cells. Because of the location, the L452R mutation is thought to make the virus better able to stick to human cells, thus making the variant more infectious.

The Mission District research was coordinated by Unidos en Salud, a collaboration between Chan Zuckerberg Biohub, UCSF, and the Latino Task Force for COVID-19. The group has been operating a rapid coronavirus testing site in the Mission District since August, and scientists have worked with the community to report on how the virus spreads there.

Erin Allday is a San Francisco Chronicle staff writer. Email: [email protected] Twitter: @erinallday

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