The health ministry of Japan temporarily suspended one more million doses of Moderna's (NASDAQ: MRNA) COVID-19 vaccine after foreign substances were found and two persons died after receiving shots from affected lots.

Japan is grappling with the worst wave of coronavirus in the country yet more than 25,000 were infected with the Delta variant. A total of 2.6 million doses were suspended in Japan, following the latest reports.

A tiny black substance was reportedly found in a Moderna vaccine vial in Gunma prefecture, an official from the prefecture said, while black and pink substances were found in syringes and vials in Okinawa.

On Saturday, the government reported that two persons died after receiving the Moderna vaccine from the affected lots that got suspended.

The government said there were no safety or efficacy issues identified regarding the vaccine and that suspension came as a precautionary measure. The causes of death are currently under investigation.

"It is unlikely, in my opinion, that contamination of foreign substances led directly to sudden deaths," said Takahiro Kinoshita, a physician and vice chair of Cov-Navi, a vaccine information group.

"If the contaminated substances were dangerous enough to cause death for some people, probably many more people would have suffered from some symptoms after the vaccination. However, further investigations are definitely needed to evaluate the harm of the particular doses in question," he added.

Shares of Moderna are down 2% on the day.