Japan put on hold the use of 1.63 million doses of US pharma giant Moderna’s COVID-19 vaccine on Thursday following reports of contaminants in some vials.

Takeda, the Japanese company that distributes the vaccine in the country, detected the contaminants on August 16, but informed the government after a week on Wednesday which means several more people must have got the shots from the contaminated lot. 

Takeda informed the government that the 7-day delay occurred as it needed time to gather information on which vials were affected and where they were in the country, a Reuters report quoted a Health ministry official as saying.

Moderna issued a statement confirming it has been notified of cases of particulate matter being seen in drug product vials of its COVID-19 vaccine. The U.S. vaccine maker said it has stopped any further distribution of the lot that was found contaminated and two adjacent lots as well.

"The company is investigating the reports and remains committed to working expeditiously with its partner, Takeda, and regulators to address this," Moderna said. Takeda Pharmaceutical is the Japanese company that distributes the vaccine in the country.

Moderna said the contamination could be due to a manufacturing issue in one of the production lines at its contract manufacturing site in Spain.

Spanish pharma company Rovi which bottles Moderna vaccines for markets other than the United States, said it is investigating possible contamination of Moderna doses and the issue appeared to be limited to a few batches bound for Japan.

The suspension comes as another setback for Moderna, which has been seeing production delays last month that disrupted supplies to countries, such as South Korea.

Both Japan and Moderna said that no safety or efficacy issues had been identified and that the suspension was just a precaution.

However, several Japanese companies including leading airlines All Nippon Airways and Japan Airlines cancelled COVID-19 vaccinations for its employees scheduled for Thursday.