The employee’s motive is unclear.
The hospital, the Aurora Medical Center in Grafton, Wis., notified the local police department, which is investigating the incident, along with the Federal Bureau of Investigation and the Food and Drug Administration, the police said.
The person responsible, whom it did not name, is no longer an employee, the hospital system said in its statement. It was not clear whether any charges had been brought. The police department said it could not comment further on an active investigation.
“We are more than disappointed that this individual’s actions will result in a delay of more than 500 people receiving their vaccine,” the hospital system, Aurora Health Care, said.
Aurora said it learned of the incident earlier this week and was originally led to believe that the spoilage was accidental. But on Wednesday, it said, the employee acknowledged intentionally removing the vials of vaccine from refrigeration.
The spoiled doses were of the Moderna vaccine, which can be stored safely at normal freezer temperatures. The other vaccine authorized for use in the United States so far, developed by Pfizer and BioNTech, must be kept much colder in special ultracold freezers.
Wisconsin experienced a devastating surge of coronavirus cases in the fall, and at times was the hardest-hit state in the nation relative to its population. Transmission has since slowed a bit, but the state is still reporting about 39 new cases a day for every 100,000 people. At least 5,195 Wisconsin residents have died.
As of Tuesday, the state had received 156,875 doses of vaccines and had administered 47,157 doses, according to the Wisconsin Department of Health Services.