Japan suspended the use of about 1.63 million doses of Moderna vaccine Thursday after contamination was found in unused vials, raising concern of a supply shortage as the country tries to accelerate vaccinations amid a COVID-19 surge.

Prime Minister Yoshihide Suga said Thursday that the government’s decision to suspend the use of some 1.63 million doses of Moderna Inc.’s COVID-19 vaccine — a move that followed the discovery of foreign materials in one batch — will have little impact on its national vaccine rollout plans.

“I’ve received a report from the health ministry saying that it will not have a big impact,” Suga told reporters. “I have instructed the health ministry that safety is the top priority.”

Nonetheless, the incident is another bump in the road for Suga’s goal of completing both rounds of vaccination for 80% of all residents by early October.

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. 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 Japanese government has signed a contract for 50 million Moderna shots by the end of September. So far, about 18 million Moderna doses have been used, mainly at mass inoculation centers run by the central government and prefectures, since May.