Michigan admits underreporting 200K+ COVID-19 cases, many during worst wave

• Michigan officials in October corrected an accounting error that led to the underreporting of 200,000 COVID-19 cases since 2020
• During the omicron wave in 2021 and 2022, weekly case counts were 25% to 30% higher than what was reported at the time
• State officials say the mistakes didn’t change death counts or overall trends, while Republicans renewed criticism of Gov. Gretchen Whitmer

Michigan underreported tens of thousands of new weekly infections during the worst wave of the COVID-19, an error that state officials didn’t correct until last month.

The Michigan Department of Health and Humans Services in October revised the onset date of roughly 200,000 COVID-19 infections and acknowledged to Bridge Michigan that, prior to those changes, the state had misreported the timing of roughly 6% of the 3.3 million cases since the pandemic began in March 2020.

The state blamed the problem on a computer error, saying that as people got COVID-19 for a second or third time, some new infections were considered a “reinfection” and were assigned to the date of that person’s  earlier illness.

That led to lower reported case counts including during the massive omicron wave, with the state reporting up to 30% fewer infections each week than which were actually occurring.

For January 2022, the state had reported 391,000 infections; that’s now been revised to over 491,000, or 27% more cases.

Officials in the administration of Gov. Gretchen Whitmer, a Democrat, say the mistake didn’t change the public's perception of the pandemic, death tolls or the arc of waves. No statewide restrictions were in place when the highest number of cases were misreported.

Related:

• Free COVID tests return in time for Michigan’s respiratory disease season
• Michigan repurposes COVID testing sites to reduce health disparities
• School is back in Michigan. So is COVID-19. What to know

“Overall trends reported in recent years were representative of COVID-19 illness activity, but specific counts by days displayed on the dashboard may have had underreported case totals,” said Lynn Sutfin, a spokesperson for the Michigan Department of Health and Human Services, in an email to Bridge.

She added that "at the time (of the mistake,) vaccines were widely available, and case numbers did not affect public health recommendations."

Sutfin said an internal review of data discovered the error and the state notified a computer vendor about the “data anomaly” in August. The mistake was fixed on public dashboards on Oct. 8. 

Bridge Michigan discovered the changes during a routine check of the data, which it has long monitored, and asked state health officials about the shift in cases.

One Republican leader told Bridge the new revelations of underreported cases are cause for concern.

"This is a reminder that before, during, and since the pandemic, the Whitmer administration has repeatedly fumbled the ball in basic governance,” state House Minority Whip Mike Harris, R-Waterford, said in a statement. 

“Despite these failings, the bureaucracy has avoided oversight as Democrats have looked the other way."

The mistake follows disagreement about death counts in nursing homes during the early months of the pandemic. In 2022, the state’s auditor general authored a report claiming that Michigan had 42% more deaths in long-term care facilities (8,061 vs. 5,675.)

Whitmer’s administration questioned the report’s accuracy. Last year, Whitmer proposed cutting the Auditor General Office’s budget by 28%, prompting accusations of retaliation.

Bridge left messages seeking comment from Whitmer’s office and legislative Democrats. They were not returned.

The underreporting did not change the bottom line of cases, just the timing, and death reports were not affected. Some 45,500 people have died from COVID-19 statewide. Nationwide, the toll is 1.2 million.

Marisa Eisenberg, an epidemiology professor at the University of Michigan, told Bridge that she doubts the discrepancies would have affected “any major policy.” 

“But of course you want the data to be as accurate as possible,” said Eisenberg, who worked closely with the state on data modeling during the pandemic.

Eisenberg said she was unaware of the revision but said researchers will want the updated data because they are still trying to make sense of the pandemic.

“We’re going to be trying to understand the pandemic for a long time,” she said.