The Gunma prefectural government said Sunday that foreign substances were discovered in Moderna Inc.'s COVID-19 vaccine, the latest in a series of contaminants in the company's product reported in Japan over the past several days.

Blackish foreign matter, less than 0.5 millimeters in size, was spotted during pre-inoculation inspections in a vial that has a different lot number from those of the three lots suspended Thursday for use and another found Saturday in Okinawa containing black and pink substances.

About 4,500 people received shots in Gunma under the lot number over the three days through Sunday but no cases of ill health have been reported, the local government said.

Gunma becomes the seventh prefecture to report the discovery of foreign matter in the Moderna vaccine following Ibaraki, Saitama, Tokyo, Gifu, Aichi and Okinawa.

All the seven are among 21 prefectures, out of the total 47, currently under a COVID-19 state of emergency, as Japan is struggling to contain a spike in coronavirus infections.

The same day, the Okinawa prefectural government said it halted inoculations at a mass vaccination site in Naha following the discovery of contaminants in a vial and three syringes filled with vaccine from three different vials.

These four vials fall under the same lot number -- 3005293 -- which is different from the three other lot numbers identified by Japan's health ministry Thursday as potentially contaminated doses.

The Health, Labor and Welfare Ministry said Sunday that rubber pieces have likely fallen into the vials when a syringe needle was inserted into the rubber top of the vials. The ministry has found no major problem in vaccine quality, it added.

The ministry said it consulted with Japanese drugmaker Takeda Pharmaceutical Co., which is in charge of the sale and distribution of the Moderna vaccine in the country, and decided there is no need to halt the use of the batch as there are no major safety issues.

About 880 people received shots in Okinawa under the lot number and the local government has not received any reports of health issues.

The contaminant issue started Thursday when the ministry said foreign substances have been confirmed in 39 unused vials at eight vaccination sites in Ibaraki, Saitama, Tokyo, Gifu and Aichi.

The ministry the same day halted the use of around 1.63 million doses of the three lots, which came from a Spanish manufacturer for Moderna, as a precaution.

Moderna launched a probe into the three lots -- 3004667, 3004734 and 3004956 -- while urging medical institutions and other entities not to administer any vaccine showing abnormalities, even doses not subject to the suspension.

The Okinawa government said it will resume inoculating people at the site on Monday and Gunma restarted vaccination at the center Sunday, both by using unaffected vaccine.

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