SAN FRANCISCO (CBS SF) — The first California cases of a South African variant of the COVID-19 virus have been found in the Bay Area.

Gov. Gavin Newsom made the announcement at a press conference Wednesday in Fresno to update the state’s vaccine response and unveil a new vaccination site for the Central Valley.

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“As of a few hours ago, we have the first reported cases of South African variants,” said Newsom. “Two cases have been reported at Stanford, one in Alameda and one in Santa Clara County.”

According to local health officials, the Santa Clara County case involves an individual who recently returned from international travel with another person in their household last month and experienced symptoms several days later. Officials said the pair followed the county’s 10-day mandatory travel quarantine and remained isolated in their apartment for the entire period they were potentially infectious.

Santa Clara County Public Health Officer Dr. Sara Cody praised the individual, adding the person had food delivered and never left their apartment.

“This is an important example of how public health measures can help break the chain of transmission and why it is critical that, we, as a community continue to avoid travel and quarantine upon return,” said Cody.

The other household member also became ill, she said, and is presumed to have had COVID-19, but did not get tested.

“They were not infectious when they were traveling, their infectious period started when they were back home,” Cody said.

Meanwhile, the case in Alameda County remains under investigation.

Cody said that not all positive COVID-19 results are sequenced for variants.

“In some ways we sort of have to assume that perhaps these variants of concern are already circulating,” said Cody. “We just don’t know to what extent.”

Catherine Blish, an associate professor of medicine at Stanford University, said the United State lags in sequencing for variants.

“It’s not an easy thing to test exactly which variant it is,” Blish said. “It’s both expensive and time consuming.”

She said, however, that it’s no surprise the South African variant has appeared in California.

“I do want to stress variants happen,” Blish said. “This is what viruses do and the more infections there are, the more opportunities the virus has to generate new variants.”

It’s why experts are emphasizing the need to prevent infections with vaccinations, mask wearing and handwashing.

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The South African 501Y.V2 variant is one of several recent mutations of the virus, most of which involve changes to its spike protein — the part of the virus that enables it to enter human cells — that may make it more contagious and slightly more resistant to vaccines.

The variant has been found in other parts of the U.S. and in 36 other countries. It was first detected in the United States in South Carolina in January.

Newsom also said there were 159 cases of the U.K. variant and 1,203 cases of 2 types of West Coast variants in California.

Earlier this week, the head of the World Health Organization said the emergence of new COVID-19 variants has raised questions about whether existing vaccines will work. On Sunday, South Africa halted use of the AstraZeneca-Oxford vaccine after evidence showed it was not effective against the variant first seen there.

National Institute of Allergy and Infectious Diseases Director Dr. Anthony Fauci said the U.K. variant would become the dominant strain in the U.S. by the end of March, and that vaccines from Moderna and Pfizer are still effective against that variant, but less so against the South African variant.

Fauci warned about delaying the second doses of the Moderna and Pfizer vaccines, saying doing so would allow for more mutations of the coronavirus.

“The way viruses respond to pressure, you could actually be inadvertently selecting for more mutants,” Fauci said Monday at a White House coronavirus briefing. “For that reason, we have continued to go by the fact that we feel the optimum approach would be to continue with getting as many people on their first dose as possible but also making sure that people — on time — get their second dose.”

California has administered 5.1 million vaccines out of 7.6 million doses delivered to entities within the state. During his news conference at the Fresno County Fairgrounds, Newsom announced a new vaccination site at Fresno City College. A proposed mass vaccination site at the Save Mart Center has not yet gotten approval from the federal government.

During the news conference, hecklers could be heard saying “recall Gavin” from a distance.

The emergence of the variant was not unexpected. But will it shift the virus fight strategy?

“This was a known known,” UCSF Epidemiologist George Rutherford told KPIX 5. “It just intensifies our strategy.”

The strategy right now is vaccinations as fast as supply will allow. They were hoping to hit 1,000 Wednesday at the recently-opened vaccination site Levi’s Stadium, the largest in California.

Increased emergence of the variant will likely prompt more calls for accelerating 1st shots, with the addition of booster shots down the road. But considering the numbers may still be small, there is another possible strategy.

“This is something, if there are really only a couple of cases, which may mean that there are you know tens of cases, we might be able to get around them and do enough contact tracing and isolation to control it,” Rutherford says of a possible containment approach. “And I’d be very much in favor of that.”

California announced Wednesday the state has had 3,362,981 confirmed COVID cases to date, with 8,390 newly recorded confirmed cases Tuesday. There have been 44,995 COVID-19 deaths since the start of the pandemic.

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Newsom said the state has reported progress in every category, noting a 13.9% positivity rate from 30 days ago dropping to 4.8% as of Wednesday 13.9%, along with a 34% decline in hospitalizations and a 28% drop in ICU admissions.