Japan’s health ministry and drugmaker Takeda will halt the use of 1.63 million doses of Moderna’s COVID-19 vaccine after reports of contamination in several lots.

Takeda, which is in charge of sales and distribution of the Moderna shot in Japan, said it had “received reports from several vaccination centers that foreign substances have been found inside unopened vials from specific lots.”

“Upon consultation with the health ministry, we have decided to suspend the use of the vaccine from the lot from August 26,” it added.

The firm informed Moderna and “requested an urgent investigation.”

Takeda did not detail the nature of the contamination, but said it had not so far received any reports of health concerns arising from affected doses.

The health ministry said it would work with Takeda to secure alternative doses to avoid disruption to the country’s vaccine rollout, which has ramped up after a sluggish start.

Around 43 percent of Japan’s population is currently fully vaccinated, but the country is battling a record surge of virus cases driven by the more contagious Delta variant.