BERLIN - Almost 9,000 people in the municipality of Schortens in northern Germany could have received saline instead of a COVID-19 vaccine, the county of Friesland said on Tuesday.

At the end of April, it was revealed that an employee at a vaccination center had filled at least six syringes with saline solution instead of the BioNTech/Pfizer vaccine.

Further investigations by police suggested "that these are not isolated cases," Friesland district administrator Sven Ambrosy said. "Unfortunately, we have to consider the possibility that many more people are affected."

Police said that the suspect, who was subsequently dismissed, had shared conspiracy content on social media, and openly criticized measures taken by the government to tackle COVID-19.

"In this unclear situation, it is important that all those who may have been affected are offered catch-up vaccinations in a timely manner," said Matthias Pulz, president of the Lower Saxony State Health Office. "This is the only way to safely ensure complete vaccination protection."

As of Tuesday, more than 45.8 million people in Germany were fully vaccinated, bringing the country's vaccination rate to 55.1 percent, according to the Robert Koch Institute (RKI), the federal government agency for disease control and prevention.