California is now the 4th state to report cases of the more infectious coronavirus variant found in South Africa

• California is the latest state to report cases of the more transmissible coronavirus variant found in South Africa
• The variant, first identified in in October, has been found in at least four US states.
• The variant seems to partially evade immunity gained in response to vaccines or infection with the original virus.

Once South African scientists detected a more infectious coronavirus variant in early October, scientists knew it was only a matter of time before the strain reached the US.

At the end of January, the US reported its first two cases of the new variant, called B.1.351, in South Carolina.

California became the latest state to report its own B.1.351 cases on Wednesday. At a press conference, Gov. Gavin Newsom said Stanford University had detected two cases in the San Francisco Bay Area: one in Alameda County and another Santa Clara County. He did not provide further details.

The Centers for Disease Control and Prevention has also identified six cases of B.1.351 in Maryland and one in Virginia.

The variant isn't spreading as widely as B.1.1.7, another more infectious strain first identified in the UK in September. The CDC has reported more than 930 cases of B.1.1.7 across 34 states so far.

Coronavirus vaccines still appear to be highly effective against B.1.1.7, but scientists are more concerned about B.1.351 because preliminary research found it can partially evade the protection offered by current vaccines.

Moderna, for instance, exposed blood samples from people who'd received the company's vaccine to B.1.351. They found those samples developed six times fewer virus-neutralizing antibodies than samples exposed to other variants. The company is now exploring the possibility of a booster shot that's tailor-made to neutralize B.1.351.

Scientists also worry that people who already had COVID-19 could get reinfected with this more transmissible strain.

A race to keep B.1.351 from spreading

The US genetically sequences just 0.01% of its coronavirus cases - around three out of every 1,000 cases. That puts the country 33rd in the world for genetic sequencing, according to the latest data from GISAID, a global database that collects coronavirus genomes.

This sequencing deficit means new variants can easily spread undetected in the population. In all likelihood, B.1.351 entered the US long before South Carolina reported its first cases. Neither of those people had recently traveled, nor was there any personal connection between them.

Even people who previously got COVID-19 could be susceptible, evidence suggests. A recent study of Novavax's vaccine candidate found that B.1.351 cases were just as common among people who'd previously recovered from infections with other strains as those who had not.

"If it becomes dominant, the experience of our colleagues in South Africa indicates that even if you've been infected with the original virus, that there is a very high rate of re-infection," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNN last week.

That possibility, combined with B.1.351's increased transmissibility, could lead to another rise in coronavirus cases, scientists warn. The variant doesn't appear to be deadlier than the original strain, though.

"When you have more contagious variants circulating and people now feeling free to do things that they weren't able to do for a while, we do risk having another surge happen in the near future," Anne Rimoin, an epidemiology professor at UCLA's Fielding School of Public Health, recently told Insider. "So we need to be watching it carefully."

For now, scientists hope that vaccinations and other public-health measures will be enough to keep B.1.351 from becoming the dominant strain in the US. More genetic sequencing, they add, could prevent future variants from spreading.

"We've got to find ways to get in front of this as opposed to constantly chasing behind it without good surveillance," Rimoin said. Otherwise, she added, "we're destined to make the same mistakes."