The Cook County Department of Public Health announced last week it had updated data on its COVID-19 statistics website, which is updated every weekday and tracks daily new cases, the number of cases per 100,000 population, recent percent change in case rates, and vaccination rates.

In doing so, the county dramatically altered the total number of COVID-19 cases and the vaccination rates in Riverside and North Riverside, which share the same ZIP code.

“We have finally been able to geocode every single person’s address so we can be clear that the municipal data denominators are correct,” said Dr. Rachel Rubin, co-lead and senior medical officer for the Cook County Department of Public Health, during a press conference held via Zoom on Nov. 3.

Rachel Rubin, MD, IM, Occ. Med.

Rubin specifically called out Riverside and North Riverside as towns where data had been incorrectly entered since the county began tracking COVID-19 penetration in March 2020. 

The Landmark reported previously that vaccination rates the county was reporting for the two villages might be skewed due to sharing the same ZIP code. Prior to last week, the county had reported that more than 80 percent of Riverside residents and just about 40 percent of North Riverside residents had been fully vaccinated.

That suspicion turned out to be correct. With the new data unveiled last week, the Riverside vaccination rate dropped, while North Riverside’s rose.

As of Nov. 8, the county was reporting that 64.2 percent of Riverside residents had been fully vaccinated and 58.9 percent of North Riverside residents.

“You’ll see that the North Riverside data looks better [in terms of vaccination rate] and Riverside looks a little worse, and that’s because we’re actually mapping people according to where their municipal home really is,” Rubin said.

In addition, total case numbers in each village shifted significantly with the release of the newest data. On Nov. 2, the county reported that Riverside had recorded 1,124 cases of COVID-19 since March 2020 and that North Riverside had recorded 735.

In the wake of last week’s shift in data, as of Nov. 8 the total number of COVID-19 cases recorded in Riverside since the pandemic started in March 2020 stood at 891, while the number recorded in North Riverside leapfrogged past Riverside’s total to 977, showing the pandemic actually hit North Riverside harder than initially reported.

Of the three villages covered by the Landmark, North Riverside now has recorded the highest number of COVID-19 cases per 100,000 people at 13,156. Riverside’s is the lowest of the three at 9,583, while Brookfield’s is 11,614.

“There have been some incorrectly entered addresses with communities that have similar names, like Riverside and North Riverside,” Rubin said. “Geocoding also corrects that.”

The county at the same time also announced that it was now measuring vaccination rates based on 2020 census data, which had the effect of slightly lowering the vaccination rate in Brookfield, where the population grew by about 500 people compared to 2010.

Whereas Brookfield’s percentage of fully vaccinated residents was listed at nearly 62 percent at the end of October, the rate for full vaccination in Brookfield on Nov. 8 was listed at 60.1 percent.

Rubin said the county’s goal is to concentrate vaccination efforts in the 70 municipalities in suburban Cook County where the single-dose vaccination rate has not yet reached 70 percent.

“One thing the new data shows us is that we can really see a cut point of how many municipalities have had less than 70 percent [of the population receiving at least one dose of the vaccine], which is our new goal,” Rubin said.

With the new data, the first-dose vaccination rates in Brookfield (73.4 percent), Riverside (78.7) and North Riverside (70.9) all meet that 70-percent target.

The data shift reported last week did not affect the total number of fatal cases of COVID-19 reported in any of the communities covered by the Landmark. That information is tracked separately by the Cook County Medical Examiner. While the Landmark has noted some Riverside/North Riverside address discrepancies over the past 20 months, they are rare and are easier for the Landmark to catch.