FORT MADISON, Iowa (AP) — The Iowa Department of Corrections says nursing staff at a Fort Madison prison incorrectly gave 77 inmates overdoses of the Pfizer COVID-19 vaccine, and now, administration of coronavirus vaccines at the prison have been halted.

The Des Moines Register says the incident happened Tuesday. Department spokesman Cord Overton told the newspaper that once the error was realized, staff immediately sought guidance from the federal Centers for Disease Control and Prevention and from Pfizer.

Overton says the inmates were notified and are being closely monitored by medical staff. He says the inmates affected have so far shown only the side effects commonly associated, including soreness at the injection site, body aches, fatigue and fever.