Four cases of the omicron variant of COVID-19 have been identified in the District, officials announced Sunday in a news release from DC Health.

All four cases — three adult women and one adult man — are unrelated to each other. Three involved people who had recently traveled outside of the District, making trips to Florida and New York, Virginia, and Maryland. DC Health says it has been in touch with all close contacts of three of the cases.  There were no known exposures or close contacts for one person.

All four of the individuals were fully vaccinated. One woman was known to have been eligible to get a booster shot, but hadn’t received it yet. The other three cases’ booster status was unknown.

One of the cases was affiliated with Georgetown University, according to an announcement from the university. The person, who is currently asymptomatic, had not been on campus since the Thanksgiving holiday, except to take a coronavirus test. The university conducted the test, and the sample was sequenced by a lab at the National Institutes of Health.

“There is no indication that transmission occurred on our campus. Georgetown’s weekly positivity rate still remains below 1%, even as we conducted more than 15,000 tests of students, faculty and staff in the weeks following the Thanksgiving holiday,” the university’s announcement continues. “Any Georgetown community members who test positive for COVID-19, including the Omicron variant, will continue to be notified by our contact tracing team and given instructions for isolation.”

DC Health said the news of the presence of the omicron variant underscores the need for residents to take precautions to avoid getting sick.

“The recent emergence of the Omicron variant further emphasizes the importance of vaccination, boosters, and prevention strategies (e.g. masking, washing your hands frequently, choosing activities wisely, and physically distancing from others) needed to protect against COVID-19,” the department said in the news release.

Cases of the omicron variant have been previously identified across the region, first in Maryland and then in Virginia. In Maryland, two of the cases appeared in a household where someone had recently traveled to South Africa, the country where the variant was first identified. In Virginia, the commonwealth’s first case had only traveled domestically.

There could easily be more cases of the omicron variant in the region, too. To identify just one, scientists have to perform genomic sequencing on existing positive coronavirus test samples. As always throughout the pandemic, there are days-long lags in time between infection and detection of the virus, making it impossible for public health experts to know exactly how many cases of the virus or the variant there are in the community at any given time.

The World Health Organization listed the omicron variant as a “variant of concern” in late November. The classification came after public health experts saw a significant rise in cases in South Africa that coincided with the variant’s detection (cases in South Africa exploded from a few hundred new ones per day in mid-November to about 4,500 per day recently). Early data suggests that omicron may be even more transmissible than the highly transmissible delta variant. Delta is still the dominant variant in the U.S., making up for 99.9% of infections, according to CDC estimates.

There are also concerns that the variant’s many mutations might help it evade existing vaccines, particularly vaccine protection against initial infection. Vaccines are still thought to protect against severe disease caused by the omicron variant.

Health officials in the D.C. region and around the country are calling for anyone eligible for a booster shot — that is, adults and children 16 years and older who are 6 months out from their initial course of the vaccine — to go out and get one as soon as possible. The heightened immunity resulting from a booster may help recoup some of the effectiveness of the vaccines against the omicron variant.

It’s not yet clear if the omicron variant causes more severe illness than other strains of COVID-19, but there are some early indications that existing cases linked to the variant have been mild.