"This omicron variant is real. It is spreading," Lightfoot said.
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The mayor and other city officials once again encouraged unvaccinated residents to get the shot while visiting a Chicago family vaccination clinic at Wilbur Wright College on the Northwest Side.
"It's even more important to get vaccinated and boosted," said City Colleges of Chicago Chancellor Juan Salgado.
While the Omicron variant has not been reported in Illinois yet, Chicago public health officials said that could change soon.
"We know there are people who have been exposed to the Omicron variant," said Chicago Department of Public Health Commissioner Dr. Allison Arwady.
The new variant is twice as contagious as the Delta variant. Sunday morning's concerns follow the Thanksgiving holiday and come as Chicago remains in the grips of a surge in COVID cases. The city reported more than 1,300 new COVID cases Monday, breaking the record set back in January.
"We can beat this virus, but it's a collective effort. All of us have to be involved," said Alderman Roderick Sawyer, who chairs the Chicago City Council's Health and Human Relations Committee.
Despite the threat of Omicron, city officials said at this point, they're not making plans for any large scale pull back with schools or the city. They have instead increased efforts targeting underserved neighborhoods and the unvaccinated and un-boosted, like Regin Igloria, who got his shot Sunday.
"I'm doing whatever precautions are necessary," said Igloria.
The city has also started expanding its vax-at-home program to seven days per week and began hosting weekend pop-up vaccinations sites.