TOKYO -- Vials of coronavirus vaccine developed by Moderna contained particles of stainless steel, the U.S. drugmaker said Wednesday in a statement with Japanese distributor Takeda Pharmaceutical, revealing why roughly 1.6 million doses in Japan were withdrawn.
The particles do "not pose an undue risk to patient safety," and they "are unlikely to result in other adverse reactions beyond the local site of the injection," according to the statement.
The statement, which follows an investigation by Takeda, Moderna and the vaccine maker's Spanish production partner, comes after reports of particulate matter in vials prompted Japan's health ministry to halt injections from the lot in question on Aug. 26. Two other lots produced at the same plant around the same time also were withdrawn.
A Takeda spokesperson also said there were "no safety problems" with the vaccine.
Two people in Japan who received doses from these lots later died. The companies called the deaths "tragic" but said they appear to be "coincidental," with no evidence connecting them to the vaccine.
"It is important to conclude a formal investigation to confirm this," the statement said. "The investigation is being conducted with the greatest sense of urgency, transparency and integrity and is of the highest priority."
The stainless steel particles likely came from improperly aligned components on the vaccine bottling line, the companies said. The problem was limited to the three lots already withdrawn, according to the statement.
Takeda begins a recall of the three lots on Thursday.
The health ministry said it will consider any administrative actions against Takeda, Japan's biggest drugmaker, based on the findings of the investigation.
All Nippon Airways and a number of local governments halted use of the Moderna inoculation after the ministry's Aug. 26 action. The Moderna vaccine was granted emergency-use authorization in Japan in May.