More than 20 people across 11 U.S. states have tested positive for the omicron variant of the virus that causes Covid-19. The patients range in age, vaccination status and travel history, but none of them have developed severe disease so far.

While some patients had recently traveled in southern Africa, where the variant was first detected, others had no travel history, indicating that community transmission is underway in the U.S.

“We absolutely have community spread in this country,” Dr. Anthony Fauci told Bloomberg Television on Friday. “We don’t know how many of them, but there’s no doubt there’s community spread.”

Scientists and public health officials are still collecting data on whether omicron is more transmissible, better evades immune protection from vaccines, and/or causes more severe disease than other variants.

Those who have tested positive in the U.S. have all shown mild to moderate symptoms and none of the patients have been hospitalized so far, according to the most current information from state public health departments. However, mild cases of Covid can progress to more severe disease over time.

Many of the people who have tested positive in the U.S. were fully vaccinated. At least two of the patients who were immunized had not received booster shots yet, but another person had received their additional dose. And in at least one case, a person who had previously recovered from Covid tested positive for omicron.

While the handful of cases in the U.S. don’t provide any definitive answers about omicron, the World Health Organization said Friday that early data suggests the virus is more contagious. And South African scientists published a study, which has not yet been peer reviewed, that found omicron carries a higher risk of reinfecting people who previously caught Covid than past variants.

Although some of the people who tested positive for omicron were fully vaccinated, the fact that they have developed mild symptoms suggests that the shots are still providing protection against severe disease from the variant, U.S. health officials said. Fauci said Friday during a White House Covid briefing that lab studies indicate booster shots increase antibody protection against a range of variants.

“There’s every reason to believe that if you get vaccinated and boosted that you would have at least some degree of cross-protection,” Fauci said, “very likely against severe disease, even against the omicron variant.”

California confirmed the first U.S. case of omicron Wednesday in a person who recently returned from South Africa to the San Francisco area. The person was between 18 and 49 years of age, fully vaccinated and was not eligible for their booster shot yet, according to Gov. Gavin Newsom. The person showed mild symptoms and is expected to make a full recovery, Newsom said Wednesday.

“The evidence that an individual with omicron identified by sequencing actually has mild symptoms, is improving, I think is a testimony to the importance of the vaccinations,” said Dr. Mark Ghaly, California’s Health and Human Services secretary.

California confirmed a second omicron case Thursday in the Los Angeles area. That adult was also fully vaccinated and had recently returned from South Africa via London, according to the city health department. The person’s symptoms are improving without medical care, officials said.

“This infection is most likely travel-related,” the Los Angeles County public health department said. The department, citing privacy concerns, would not disclose the person’s age or booster status when asked by CNBC on Friday.

In Minnesota on Thursday, public health officials confirmed an omicron case in an adult male who was fully vaccinated and had recently returned from an anime convention at the Javits Center in New York City. His symptoms were mild and have since resolved, according to the state health department.

The Minnesota resident had received a booster shot prior to attending the convention in New York, Minnesota public health spokesman Doug Schultz told CNBC on Friday.