Japan is investigating the deaths of 2 men in their 30s who died after their second doses of the Moderna vaccine

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• Two Japanese men in their 30s died after receiving Moderna doses from a batch that had been suspended by the Japanese government.
• The batches were suspended after 500,000 doses from the lots had already gone out.
• The men had no underlying health conditions or a history of allergies, but authorities say they have yet to determine a causal relationship between their deaths and the vaccines.
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Japan is investigating the deaths of two men in their 30s who died several days after being given their second shots of the Moderna vaccine.

The two men, aged 30 and 38, did not have any underlying health conditions and had no history of allergies, said the Ministry of Health, Labor, and Welfare in a statement on Saturday.

It is still unknown if there is a causal relationship between the vaccines and the two deaths, said Japanese health minister Norihisa Tamura to local broadcaster NHK on Sunday, vowing a "swift" investigation into the matter.

The men's doses came from one of the three vaccine lots whose distribution was paused by Japan last Thursday on suspicion of contamination. The country halted the use of 1.63 million Moderna shots after medical professionals reported 39 instances of foreign particles being found in vaccine vials from one lot.

By then, Japan had already administered 500,000 jabs from the potentially contaminated batches, said Taro Kono, the minister in charge of Japan's vaccination drive, according to Kyodo News.

The lot from which the two deceased men received their shots had no foreign particles reported, but it was suspended out of caution because it was produced in Spain around the same time, said authorities.

The detected foreign substance is thought to have been tiny metal particles, but health experts in Japan said it is unlikely that the pieces would have caused substantial health issues even if they were injected into the body, reported The Japan Times.

On Saturday, Moderna, Inc., and Takeda Pharmaceutical, the distributor for the vaccines in Japan, released a joint statement saying that an investigation into the contaminated vials is being "conducted with [the] greatest sense of urgency, transparency, and integrity and is of the highest priority."

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

Moderna and Takeda did not immediately respond to Insider's request for comment and updates on the investigation.