A contaminant found in a batch of Moderna COVID-19 vaccines delivered to Japan is believed to be a metallic particle, Japanese public broadcaster NHK reported, citing sources at the health ministry.

Japan on Thursday suspended the use of more than 1.6 million doses shipped to hundreds of vaccination centres nationwide, more than a week after the domestic distributor, Takeda Pharmaceutical received reports of contaminants in some vials.

The NHK report, published late on Thursday, cited ministry sources as saying the particle reacted to magnets and was therefore suspected to be a metal.

Moderna has described it as “particulate matter” that did not pose a safety or efficacy issue.

An official at the health ministry said the identity of the contaminant has not been confirmed.

Source: VOV5