Japan's health ministry said Thursday that contaminants were found in some unused doses of Moderna Inc.'s COVID-19 vaccine and the use of around 1.63 million doses from the same production line has been suspended as a precaution.
At least 180,000 potentially contaminated shots have already been administered in 19 of the country's 47 prefectures including Tokyo and Osaka, according to a Kyodo News tally based on local government reports.
Both Moderna and Japanese drugmaker Takeda Pharmaceutical Co., which is in charge of the sale and distribution of the vaccine in the country, said they had not received any reports regarding safety issues.
"To date, no safety or efficacy issues have been identified," Moderna told Kyodo News, adding it is "carefully assessing this matter and at this point does not have further comments on root causes."
Regarding possible problems in other countries, the U.S. company said, "On an ongoing basis, Moderna monitors and expeditiously assesses questions we receive about our products from global markets."
"Local authorities will make their own decisions about disclosure of information following these assessments," the company said.
Prime Minister Yoshihide Suga told reporters, "I have been briefed by the health ministry that it will not have a significant impact," when asked about the possibility of the suspension disrupting Japan's vaccination program.
The 1.63 million doses, which have been distributed to 863 vaccination centers, were manufactured on the same production line at the same time in Spain, and fall under three lot numbers -- 3004667, 3004734 and 3004956, the Health, Labor and Welfare Ministry said.
The Tokyo metropolitan government said around 9,100 people may have received contaminated shots at two of the vaccination sites it runs. Among other prefectures, Osaka counted about 50,000 such shots, Hyogo 41,500 and Aichi 28,000.
Some companies conducting workplace inoculations were forced to suspend their programs.
All Nippon Airways Co., which has administered about 4,700 doses bearing the lot numbers to employees and their family members, decided to suspend its program on Thursday and Friday.
Toyota Motor Corp. and East Japan Railway Co. are among companies that have received the potentially contaminated doses. But both said they will continue their programs using other doses from their stocks.
The foreign substances have been confirmed since Aug. 16 at eight vaccination sites in five prefectures -- Ibaraki, Saitama, Tokyo, Gifu and Aichi. They were found in a total of 39 vials.
Takeda reported them to the ministry on Wednesday.
The composition of the foreign matter, a few millimeters in size, has not been determined.
The "small black materials" reported to the ministry could be metallic fragments, one of its senior officials said.
Takeda has requested an emergency probe by Moderna, while urging medical institutions and other entities not to administer any vaccine showing abnormalities, even doses not subject to the suspension.
The Japanese company added it will make efforts to prevent the suspension from affecting the availability of coronavirus vaccine doses in the country.
The problem came to light at a time when Japan is struggling to contain a spike in coronavirus infections, with the government announcing a plan Wednesday to place eight more prefectures under its COVID-19 state of emergency.
While vaccinations against COVID-19 are under way in Japan, the highly contagious Delta variant of the coronavirus has sent daily reported cases surging in many parts of the country.
Over 10 million doses have already been administered in the country since the Moderna vaccine was approved for emergency use in May, according to the government.
The Japanese government signed a contract with Moderna to receive 50 million doses of the COVID-19 vaccine by the end of September. Currently people aged 12 and over can receive shots of the vaccine.
The vaccine, like the one developed by U.S. pharmaceutical company Pfizer Inc. and its German partner BioNTech SE, uses a new technology called messenger RNA, or mRNA, and is administered in two doses given four weeks apart.