As negotiations between city officials and the teacher’s union continue, Chicago Mayor Lori Lightfoot announced on Twitter Sunday night that classes will be canceled for a fourth day, on Monday.

"Out of fairness and consideration for parents who need to prepare, classes will be canceled again Monday," she tweeted.

Lightfoot said that though they have been negotiating hard, there has not been "sufficient progress" for a return to class to be announced.

"We will continue to negotiate through the night and will provide an update if we have made substantial progress," she wrote.

Chicago Public Schools, the nation’s third-largest school district, has been in talks with the teachers’ union over remote learning and COVID-19 safety protocols.

Amid the rise in COVID-19 cases due to the omicron variant, the Chicago Teachers Union wants the option of returning to remote learning, and most members are refusing to teach in person until an agreement is reached.

Rep. Alexandria Ocasio-Cortez has tested positive for COVID-19 and "is experiencing symptoms," her office said in a statement Sunday.

She is recovering at home.

Ocasio-Cortez is fully vaccinated and received a booster shot in the fall, her office said, adding that the congresswoman encourages everyone to get boosted and follow guidance from the Centers for Disease Control and Prevention.

Illinois Gov. JB Pritzker announced that Abbott Labs will provide Chicago public schools 350,000 COVID-19 tests amid the omicron surge and the impasse between the teacher's unions and the school district to return to classrooms.

"I am committed to seeing our kids and teachers safely in classrooms ASAP. I want to thank the CEO of Abbott, Robert Ford, who was committed to helping get kids back to school by providing rapid antigen tests, along with the team at SHIELD Illinois," Pritzker said in a statement Saturday.

"Together, they turned over every stone ... I appreciate their hard work, along with that of my staff who worked nonstop behind the scene to get this done," he said.

Chicago Public Schools canceled classes last week amid negotiations over remote learning and COVID-19 safety measures.

City leadership, including Mayor Lori Lightfoot, had asked teachers to continue in-classroom instruction, but 88% of the Chicago Teachers Union's leadership and 73% of its members voted last week in favor of remote education.

The state of New York has told 40 hospitals they must turn away nonessential, nonurgent elective surgeries for the next two weeks in response to low bed capacity. Most of the hospitals are located in upstate New York.

The determination was made after the hospital locations were added to the list of "high risk regions" by the state department of health due to 90% of beds being occupied according to the seven-day average.

"We will use every available tool to help ensure that hospitals can manage the COVID-19 winter surge," acting State Health Commissioner Dr. Mary Bassett said in a statement Saturday. "I want to remind New Yorkers that getting vaccinated and boosted remain the best way to protect against serious illness and hospitalization from COVID-19. Vaccination also protects our hospital system. We cannot return to the early months of the pandemic when hospitals were overwhelmed."

All of the hospitals in three regions -- Mohawk Valley, Finger Lakes and Central New York -- are included in those 40 facilities.

Dr. Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention, is standing by her agency's new quarantine and isolation guidance for COVID-19, which the nation’s largest association of physicians has criticized as "confusing."

The CDC updated its guidelines on Dec. 27, saying asymptomatic people who test positive for COVID-19 should self-isolate for five days rather than 10. In a scathing statement released Wednesday night, the American Medical Association (AMA) said the new recommendations "are risking further spread of the virus."

"The American people should be able to count on the Centers for Disease Control and Prevention (CDC) for timely, accurate, clear guidance to protect themselves, their loved ones, and their communities. Instead, the new recommendations on quarantine and isolation are not only confusing, but are risking further spread of the virus," the AMA's president, Dr. Gerald E. Harmon, said in the statement. "With hundreds of thousands of new cases daily and more than a million positive reported cases on January 3, tens of thousands -- potentially hundreds of thousands of people -- could return to work and school infectious if they follow the CDC’s new guidance on ending isolation after five days without a negative test."

But Walensky defended the new guidance, telling ABC News' Cecelia Vega in an interview Friday on "Good Morning America" that the CDC "make[s] these recommendations in the context of science, in the context of ongoing epidemiology and in the context of what is feasible in collaboration with our public health and local and state public health partners."

"I've read the AMA statement and I have deep respect for the AMA," Walenskey said, "but I will also say we've heard a lot of support for ongoing guidance from public health partners, from other clinical and laboratory partners as well."

Walensky referenced "dozens of studies" that have shown a COVID-19 patient is most infectious in the one to two days before symptoms and the two to three days after symptoms.

"So by five days after your symptoms, the vast majority of your contagiousness is really behind you," she said. "And what we say at day five then is, are your symptoms gone? Are you feeling better? Is your cough gone, sore throat gone? And if so, then it is safe to go out if you are wearing a mask all the time. And that means not going out to restaurants, not going out to gyms, not going out and visiting grandma, but really conscientiously wearing your mask for those last five days."

Walensky noted that people may choose to take an antigen or at-home test at day five, if they have access to one. But it's not required.

"If that test is positive, you should stay home for those extra five days. But if that test is negative you should go out and continue to wear your mask," she said. "You know, these tests are actually not authorized for the purpose of evaluating contagiousness."

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CDC director responds to criticisms on COVID-19 guidance