A nurse in Germany is being investigated for allegedly switching COVID-19 vaccines with saline solution.

CNN reports the nurse replaced the vaccinations between March and April at Roffhausen Immunization Center in Friesland, a rural district in Northwest Germany. Health officials claim the nurse was able to swap the vaccine out with a placebo because she was “responsible for the preparation of vaccines and the preparation of syringes during her working hours in the vaccination center.”

Sven Ambrosy, the Friesland district administrator, acknowledged the incident in a Facebook post on Tuesday.

“Today I had the sad duty to inform around 8,600 people who may have been affected that it cannot be ruled out they may have received a saline solution instead of their vaccination at their vaccination appointment,” Ambrosy said. “For peace of mind we would recommend people get an additional vaccination. I’m totally shocked by the incident. The district of Friesland will do everything possible to ensure that the affected people receive their vaccination protection as soon as possible.”