Moderna conducted an investigation into the events, in partnership with Takeda, which is responsible for the distribution of the mRNA jab in Japan, and Rovi, which operates the plant where the contamination occurred.
Takeda and Moderna’s final audit findings, released on October 1, said the most probable cause of the particles found in one of the recalled lots was linked to friction between two pieces of metal installed in the stoppering module of the production line.
This was the result of “incorrect assembly and was due to human error specific to visually misjudging the required 1mm gap between the star-wheel and the stopper” of machinery that places the tops on vaccine vials.
A total of five, sequential lots of the Moderna COVID-19 vaccine were manufactured at Rovi between June 27 and July 3. The "incorrect assembly" occurred at the changeover of the line by the plant mechanic before manufacture of the first lot, which was not resolved at the vial breakage intervention by the line operator after the filling of the third lot. This led to the issue persisting throughout the series of five batches, said the companies.
According to the report, this issue had not occurred before.
Corrective actions being implemented to prevent such an incident from happening again include improved standard operating procedures at the changeover and the utilization of a new precision tool. “These actions will be directly overseen and confirmed by Moderna, in collaboration with Takeda.”
The companies’ health assessment also concluded that the rare presence of stainless steel particles in the Moderna COVID-19 vaccine "does not pose an undue risk" to patient safety and it does not adversely affect the benefit/risk profile of the product.