Authorities in Japan said have reported another suspected case of contamination in Moderna's coronavirus vaccines, the fourth such incident less than a week.
The health ministry said on Wednesday (September 1) that contaminants in at least one of the incidents were found to be particles of stainless steel.
It added that it did not expect the incident would pose an additional health risk.
The findings were the result of an investigation by domestic distributor Takeda Pharmaceutical.
Takeda said the most probable cause of the contamination was related to friction between two pieces of metal in the machinery that puts stoppers on the vials.
The company was citing a joint investigation with Moderna and Rovi, which bottles Moderna vaccines.
The country suspended the use of over 1.6 million doses of Moderna shots last week after being notified of contamination in some of the supply.
The latest incident comes from Kanagawa prefecture, where almost 3,800 people had already received shots from the contaminated lot, but the rest is put on hold.
The Japanese government said earlier that the particles in some incidents may be pieces of rubber, caused from needles that were incorrectly inserted into vials -- breaking off bits of the rubber stopper.