Chicago's coronavirus cases are up slightly over the last couple weeks, and the city's top doctor said one age group is seeing a majority of the latest increase.
The city is now averaging 57 coronavirus cases per day. That number is up from the average daily case rate of 41 seen one week earlier, but significantly lower than the more than 200 cases per day the city was seeing just over a year ago.
"It's showing that with some new variants here, with some additional spread, you know, the risk is ever so slightly higher than it was a week ago," Arwady said. "But the difference is that for people who are fully vaccinated, that risk is very, very low. Whereas for people who are not vaccinated, especially as these case numbers go up, you know, that risk can increase from sort of a low to a moderate to a higher risk. So we're keeping an eye on it. I do expect it will probably continue to increase, hopefully slowly, hopefully staying in control, but it's why we're working on vaccinations so hard."
Arwady noted that two thirds of the city's cases in the last month have been in people under the age of 40 and one-third of hospitalizations during that time were in people in that same age group.
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"And these are people who are unvaccinated," she said.
In the last week, increases were seen particularly in people in their 30s, Arwady said.
"The case rates that have been increasing just over the last week or two are in people first in their 30s, then in their 20s and then in the kids zero to 17," she said.
According to the city's latest data, 30- to 39-year-olds saw the highest average daily case rate in the last week compared to other age groups.
Arwady's comments come as concerns surrounding the delta variant and unvaccinated residents continue to rise.
She noted that parts of Illinois are seeing a "small" surge in cases, but that it's not unexpected.
"There are whole counties far downstate that are less vaccinated than even our least vaccinated areas in Chicago," she said. "And when you have the delta variant, which is more contagious, can spread more easily, it's not unexpected to see some of this increase."
Illinois Department of Public Health Dr. Ngozi Ezike echoed those claims earlier this week in an interview with NBC Chicago.
"There is a very clear connection between where those case rates are growing the fastest and how well that area is vaccinated," Ezike said. "I.e. the more highly vaccinated areas are having lower case rates."
Cook County officials also warned Thursday that cases of the delta coronavirus variant are surging, asking residents who have not yet been vaccinated to get their shots in an effort to prevent spread.
"The variant continues to surge and while research suggests that vaccinated individuals are generally protected, we know that there are still large segments of our population that are unvaccinated and high risk this infectious variant," Cook County Board President Toni Preckwinkle said during a coronavirus update alongside health officials.
Preckwinkle noted that just under 60% of Cook County residents have received at least one dose of the vaccine.
"However 70-80% is needed to reach herd immunity," she added. "So we're a ways from that."
Health officials have said the delta variant has a higher transmissibility that impacts more people at a time than previous variants. Within weeks, Ezike said Illinois has seen COVID cases double statewide.
Studies have shown that the delta variant spreads approximately 225% faster than the original strain of the virus. Studies have also shown that once a person catches the delta variant, they likely become infectious sooner, and that the virus grows more rapidly inside a person’s respiratory tract.
Still, according to both Ezike and Cook County Department of Public Health Co-lead Dr. Kiran Joshi, vaccines are so far providing protection in the state.
"We have seen some [breakthrough cases]. Are they increasing? No," Joshi said, referring to cases in which fully vaccinated people contract COVID-19. "We know the vaccines are incredibly effective."
Illinois' top doctor said Tuesday that breakthrough cases of COVID-19 in fully vaccinated residents are a "unicorn."
"These vaccines are truly effective," Ezike said. "You know, everyone has heard of a case or two of someone who had a breakthrough infection or breakthrough hospitalization, but it is, that is so far the unicorn, that you need to focus on the people who are not vaccinated, they're the ones filling up the hospital as COVID patients."
Just over 2% of COVID-19 deaths in Illinois so far this year have been among fully vaccinated residents, known as "breakthrough" cases, according to state health officials.
A total of 151 people in Illinois have died due to COVID-19 or complications after being fully vaccinated, according to data updated Wednesday by the Illinois Department of Public Health. That figure equates to 2.2% of COVID-19 deaths in the state since Jan. 1, officials said.
At least 563 fully vaccinated people have been hospitalized in Illinois, IDPH said. The state only reports breakthrough infections among those who have been hospitalized or died, IDPH said.
A person is considered “fully vaccinated” two weeks after receiving the second dose of either the Pfizer or Moderna COVID vaccine, or two weeks after receiving the single-dose Johnson & Johnson vaccine.
The state does not publicize the number of residents who tested positive after being fully vaccinated but did not die or require hospitalization in order to "help maximize the quality of the data collected on cases of greatest clinical and public health importance," IDPH's website reads.