Suburban Cook County followed Chicago Friday in issuing an indoor mask mandate. (Antonio Perez / Chicago Tribune)

       Cook County issued an indoor mask mandate Friday as Illinois marked its highest one-day total in COVID-19 cases since late January.

       Illinois reported 4,904 new confirmed and probable coronavirus cases Friday, pushing the seven-day average of new cases above the peak of the spring surge.

       With Chicago already under an indoor mask mandate, the Cook County Department of Public Health followed suit Friday, announcing that everyone over 2 will have to be masked in indoor public spaces, regardless of whether they’re vaccinated.

       The mandate goes into effect Monday and includes a requirement for businesses to post signs on all entrances advising customers of the rule.

       Over the past week, the state has averaged 3,526 new cases per day, exceeding the average of 3,390 daily cases recorded the week ending April 13, at the height of COVID-19′s third wave in Illinois, just as vaccines were becoming available to anyone 16 or older.

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       Last week, the state was averaging 3,048 cases per day, and a month ago the average was 834 daily cases.

       The average is still well below the all-time high of 12,384 daily cases recorded the week ending Nov. 16, but at that time no vaccine had been made available to the public.

       Shoppers wear their masks while at a Uniqlo store in Chicago on Aug. 17, 2021. (Antonio Perez / Chicago Tribune)

       The latest surge in COVID-19, driven by the highly contagious delta variant, has brought on renewed restrictions, including a citywide mask mandate for indoor public places in Chicago that took effect Friday, a statewide mask mandate for schools and now the Cook County health department’s mask requirement. That department covers suburban Cook County except for Evanston, Skokie, Oak Park, and Stickney Township.

       Gov. J.B. Pritzker said Friday that while he is “deeply concerned, especially that the delta variant is having an increasingly serious medical impact on younger people,” he still does not believe another universal mask mandate is necessary statewide because numbers are not increasing “in an exponential fashion.”

       “Every time I have believed and the doctors have advised me that we need to put mitigations in place, we have done it,” Pritzker said. “And so I’m not reticent to do that.”

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       Pritzker encouraged people to get vaccinated and wear masks while in indoor public settings, which the Centers for Disease Control and Prevention recommends in areas of substantial or high coronavirus transmission. That now includes all 102 counties in Illinois, according to the latest CDC data.

       He also encouraged local communities to put in tighter restrictions, as Chicago has, when they feel it’s necessary.

       Along with COVID-19 cases, the number of people hospitalized with the disease also continues to rise statewide.

       As of Thursday night, 2,000 coronavirus patients were in hospital beds statewide, bringing the seven-day average of hospitalizations to 1,892. That’s the highest level since the week ending May 12, when an average of 1,899 patient with COVID-19 were in the hospital each day.

       During the spring surge, the seven-day average of hospitalizations peaked at 2,165 per day for the week ending April 22. The average number of coronavirus patients in hospitals reached an all-time high of 6,119 during the week ending Nov. 24 and hit a peak of 4,819 daily patients the week of May 2, 2020, during the pandemic’s initial wave.

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       The number of patients requiring intensive care and ventilators have seen a corresponding increase, also reaching levels not seen since the spring wave was subsiding in May.

       Pritzker and public health officials have stressed that nearly all patients who are ending up in the hospital with COVID-19 are unvaccinated.

       The same is true for those dying from COVID-19, officials say.

       On Friday, the state reported 18 more fatalities, bringing the overall death toll in Illinois to 23,717 since the pandemic began.

       While deaths lag behind cases and hospitalization, the average number of deaths reported per day also is on the rise.

       Illinois averaged 18 deaths per day during the past week, the highest number since the week ending June 12. The seven-day average of deaths had fallen as low as four per day in late July. Deaths peaked at an average of 155 per day in early December.

       dpetrella@chicagotribune.com

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