A 23-year-old Italian woman was mistakenly given six doses of the Pfizer BioNTech COVID vaccine at the Nora hospital in Tuscany.

Hospital spokeswoman Daniella Gianelli told CNN the patient was in “good health” with no underlying conditions, and was discharged on Monday, May 10 after being monitored for any adverse reactions for 24 hours.

The health worker who administered the shot accidentally filled a syringe with an entire bottle of the vaccine, which contains six doses.

“She saw five empty syringes and realised her mistake,” Gianelli said.

The spokeswoman said doctors would continue monitoring the patient’s immune response to the “massive dose of vaccine”.

The young woman was eligible for the vaccine before others in her age group because she is an intern in the hospital’s psychology department, Gianelli added, due to the Italian government’s decree making vaccination mandatory for all healthcare and pharmacy workers to protect medical staff, patients, and vulnerable people.

An internal investigation has been opened, Gianelli said, adding that it was “maybe just human error, definitively not on purpose”.

This article originally appeared on Over60.