Police are investigating the nurse’s actions at a vaccination centre in Friesland, near the North Sea coast.
Initially just six people were believed to have received the harmless salt solution there in March and April.
Many of those affected were aged over 70 – a high-risk group in the pandemic.
Inspector Peter Beer, quoted by Süddeutsche Zeitung, said the 40-year-old woman had been sharing “corona-critical information” on social media, criticising the government’s restrictions aimed at curbing the virus’s spread.
Regional broadcaster NDR says 8,557 people have been asked to go back for repeat vaccinations, and so far about 3,600 new appointments have been confirmed.
In April the nurse had admitted giving saline to six people to cover up the fact that she had dropped a vaccine vial on the floor.
But as the police investigation unfolded it became clear that many more people had been given saline instead of the Pfizer/BioNTech vaccine.
Police are not ruling out that a political motive could have prompted the nurse’s action, though her lawyers have rejected that and they also dispute the reported scale of the saline swap.
More witnesses are being questioned and so far no charges have been reported in the case.
Germany has seen many anti-vaccination protests.
Far-right groups are among those who reject the official data and conclusions about the spread of Covid. (Courtesy BBC)