Two people have died after being jabbed with Moderna COVID-19 vaccine shots that were among the group which was found to be contaminated, Japan’s health ministry said on Saturday.

The ministry informed through an official press release that the two men, who died within days of receiving their second Moderna shot, were in their 30s.

Each had a shot from one of the three manufacturing lots suspended on Thursday.

However, the cause of the death is still being investigated. The domestic distributor, Takeda Pharmaceutical, has received reports of contaminated vials. Soon after, Japan halted the use of 1.63 million Moderna doses shipped to 863 vaccination centres nationwide. The contaminant is believed to be metallic particles, Japanese public broadcaster NHK reported.

"At this time, we do not have any evidence that these deaths are caused by the Moderna COVID-19 vaccine," Moderna and Takeda said in a statement on Saturday. "It is important to conduct a formal investigation to determine whether there is any connection."

Interestingly, the government has claimed that the suspension of the Moderna batches was merely a precautionary measure and that no safety or efficacy issues had been identified.

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Fumie Sakamoto, the infection control manager at St. Luke's International Hospital in Tokyo, said on Saturday, "There may only be a temporal relationship between vaccination and death," Sakamoto said. "There are so many things we still don't know to make any conclusions on these two cases."

Japan has administered more than 124 million COVID-19 vaccine shots, with about 44% of the population fully inoculated.

According to the reports, in the fatalities observed on Saturday, each man had a fever the day after his second dose, two days after which they succumbed to it. There has been no evidence that their shots contained contaminants, a health ministry official told reporters.