A new report from the University of Louisville suggests Jefferson County’s COVID-19 infection rate may have been higher than what officials reported in the last week of August.

Researchers from the U of L Christina Lee Brown Envirome Institute’s Co-Immunity Project tested nearly 3,000 Jefferson County residents between Aug. 25 and Sept. 1. About 1.1% of all participants tested positive for COVID-19.

Extrapolated out, that would mean there were more than 7,200 active infections among the county’s entire population that week. That infection rate is twice as high as what officials reported in that time frame, and ten times higher than infection rates measured in April.

Aruni Bhatnagar, director of the Envirome Institute, said in a press release the results “provide a startling snapshot of the current state of the pandemic” and proof vaccines are working.

The infection rate for vaccinated participants was 0.7%. But nearly 5% of unvaccinated people in the study had COVID.

“Our population [in the study] was almost 90% vaccinated, much higher than the 64% of fully vaccinated county residents,” Bhatnagar said in the release. “In the entire cohort, vaccinated people were over 12 times less likely to be infected compared with unvaccinated people. Though in our volunteer group, 65% of the active infections were in fully vaccinated individuals who had received the vaccine earlier this year. Most reported no or mild allergy-like symptoms and did not recognize that it may be a COVID infection thus did not think they needed to get tested.”

The study found western portions of Jefferson County had the highest active infection rates and lowest vaccination rates.

Participants were also tested for natural antibodies to check for recent infections. Nearly 16% had them. Researchers said that means at least 100,000 adults in Jefferson County have had COVID-19 in the past few months.

John Boyle is a reporter and editor at WFPL news focused on Southern Indiana. He is a corps member with Report For America, a national service program that places journalists into local newsrooms.