SF Gate reports that a San Francisco resident became the first in the United States to have an identified case of the omicron variant of COVID-19, marking a new phase in a pandemic that has persisted for nearly two years, officials said Wednesday.

The individual returned to SF from South Africa on Nov. 22 and symptoms showed up Nov. 25, Gov. Gavin Newsom said at a press conference. Newsom said the person is between the ages of 18 and 49.  The person has mild symptoms that are already improving, city officials said.

“The symptoms were very mild,” said Dr. Peter Chin-Hong, an infectious disease expert at UCSF, where the genomic sequencing to identify the case was done. “It’s fitting with the other reports we’ve been hearing from around the world that people are getting mild symptoms. It’s probably the first of many many that we’ll be hearing about.”

The person had received a full dose of Moderna (two shots) but hadn’t received a booster shot, Dr. Grant Colfax, San Francisco’s director of public health, said at a Wednesday press conference. The individual is self-quarantining.

“This is not a surprise,” Colfax said. “We knew omicron was going to be here. We thought it was already here and we just had not identified it yet. So this is a cause for concern, but it is also certainly not a cause for panic. We are prepared for this in the city.”

Colfax added that there are no plans to make changes to the city’s health orders at this time.  

The Biden administration moved late last month to restrict travel from southern Africa, where the variant was first identified and had been widespread. Clusters of cases have also been identified in about two dozen other nations.

The Centers for Disease Control and Prevention was moving to tighten U.S. testing rules for travelers from overseas, including requiring a test for all travelers within a day of boarding a flight to the U.S. regardless of vaccination status. It was also considering mandating post-arrival testing.

Officials said those measures would only “buy time” for the country to learn more about the new variant and to take appropriate precautions, but that, given its transmissibility, omicron’s arrival in the U.S. was inevitable.

At the press conference in San Francisco, Colfax echoed the sentiment from officials and experts across the globe that there’s still a lot to learn about the virus.

“We don’t know how infectious it is, although there is strong likelihood that it is more infectious than delta,” Colfax said. “We don’t know how sick it will make people, but that is being studied furiously right now across the world. And we don’t know yet how effective the vaccines are protecting against transmission or serious cases and hospitalizations, but most experts I have spoken to believe that the vaccines will still be of critical importance in protecting ourselves, our families and our communities.