The vials containing the white floating matter belong to the same lot, FF5357, according to the cities of Sagamihara and Kamakura, both in Kanagawa Prefecture, and Sakai in Osaka Prefecture, the Japan Today reported.
The three cities have requested Pfizer to analyze the substances.
The contaminants were discovered at three vaccination sites in Sagamihara between Saturday and Tuesday, one site in Kamakura on Sunday and one site in Sakai on Tuesday.
The cities said they did not use the doses containing the foreign matter while continuing to administer doses bearing the same lot number that were confirmed not contaminated.
Last month, the Japanese health ministry halted the use of around 1.63 million doses of Moderna Inc.'s COVID-19 vaccine as a precaution after foreign substances were discovered in numerous vials.