Moderna Inc withheld roughly 1.63 million doses in Japan after being warned of particulate matter contamination in its COVID-19 vaccine vials, the US vaccine producer said on Wednesday.

The contamination could be the result of a manufacturing failure on one of the production lines at the company's contract manufacturing facility in Spain, according to the company.

The property with the complaints has 565,400 doses, and Moderna has put the lot and two adjacent ones on hold "out of an abundance of caution."

Moderna stated that “to date, no safety or efficacy issues have been identified,” and that it would work with its partner Takeda Pharmaceutical as well as regulators to resolve the issue.

After particle matter was discovered in a large number of vaccine vials at an injection location, Takeda stated it conducted an emergency examination.

After consulting with Takeda, the health ministry decided to remove some doses as a precaution, although it will work to minimize the impact of the removal on its immunization plans.

Prime Minister Yoshihide Suga stated on Wednesday that by the end of September, roughly 60% of the population will have been fully vaccinated and that the country has enough vaccines to administer booster doses if such a decision was made.

The news of the poisoned vials was initially reported by Nikkei, citing the health ministry.