CHICAGO (CBS) — A Chicago resident has been confirmed as the first positive case of the Omicron variant of COVID-19.

The Illinois and Chicago departments of public health reported that the Chicago resident was a known contact of someone else with a confirmed Omicron case who visited Chicago.

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The Chicago resident was fully vaccinated against COVID-19 and has had a booster dose. The resident did not require hospitalization, is improving, and has been self-isolating since their symptoms began.

Rush University Medical Center got word of the first possible case of Omicron in Chicago late last week. They ran the sample through their equipment Tuesday afternoon.

“By 3 o’clock, we were able to inform the city that it was a definitive Omicron case,” said Dr. Stefan Green of the Regional Innovative Public Health Laboratory. “But you know, with one case, you can’t really say anything about transmissibility or disease severity.”

Public health officials are conducting further contact tracing.

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“Scientists need time to learn more about the Omicron COVID-19 variant, but in the meantime, we already know how to be vigilant,” Gov. JB Pritzker said in a news release. “So, get your vaccine, get your booster, wear your mask indoors, wash your hands, and get tested for COVID-19 if you feel sick or have been exposed to someone who tested positive. I encourage all Illinois residents to make a plan for how to best protect themselves and their loved ones, especially in the holiday season.”

“The City and CDPH continue to closely monitor the Omicron variant and work with medical experts to better inform our residents,” Mayor Lori Lightfoot said in the release. “To meet the urgency of this moment, it’s crucial that our residents continue to get vaccinated and receive their booster shot. We are committed to distributing the vaccine as widely and equitably as we can across our city through community-based clinics, City-run clinics, and our recently expanded Protect Chicago At Home program.”

South African authorities first reported the Omicron variant to the World Health organization on Nov. 24, but retroactive testing confirmed the variant in Europe at least five days before that. The variant contains numerous mutations and has been classified as a variant of concern.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said early research shows Omicron is likely not more severe than the now-dominant Delta variant – but it may prove to be more transmissible.

Meanwhile, new data from South Africa shows the Pfizer vaccine may have a harder time fighting off Omicron. Researchers tested people who already had COVID and now have Omicron.

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The research indicates that Omicron can get around antibodies generated by the Pfizer vaccine, but the vaccine can still neutralize the virus. But in order to fight if off, scientists say you may need the power of a booster.

CBS 2 Chicago Staff