German authorities are now advising thousands of people to get another Covid-19 jab in case they received the dummy earlier this year.
A German Red Cross nurse is suspected of injecting salt solution into people's arms instead of genuine Covid-19 vaccinations at a centre in northern Germany.
"I am totally shocked by this episode," Sven Ambrosy, a local councillor, said on Facebook as local authorities issued the call on Tuesday to about 8600 residents who may have been affected.
"Today I had the sad duty to inform around 8600 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.
"For peace of mind we would recommend people get an additional vaccination," Ambrosy said.
The nurse was able to replace vials because she was "responsible for the preparation of vaccines and the preparation of syringes during her working hours in the vaccination centre", health authorities said.
It's unknown why the shot-blocker nurse had injected people with blanks; however, she had reportedly broadcast anti-vax views on social media, investigators reported.
Police found the nurse involved was "motivated to oppose the vaccination".
"Since she remains silent with police, we do not know whether and to what extent she was manipulated during this period," said Claudia Schröder, the deputy head of the Lower Saxony coronavirus team.
While saline jabs are harmless, the elderly patients who received it instead of a real vaccine will be at high risk from Covid.
Police investigator Peter Beer, speaking earlier at a news conference covered by German media, said that based on witness statements there was "a reasonable suspicion of danger".
