About 3,790 people have already been vaccinated from this batch of Moderna. However, after the detection of foreign impurities, the immunization of the population with this vaccine was suspended.

Japan reported another incidence of contamination with Moderna’s COVID-19 vaccine, the fourth in less than a week, threatening to halt the country’s sputtering vaccination campaign.

Kanagawa prefecture announced Tuesday that some black particles were discovered in one Moderna vaccine vial during a routine screening for foreign substances before to use, and the remainder of the batch has been halted.

Japan halted the use of 1.63 million doses of Moderna shots last week after receiving notification that some of the supply was contaminated. Moderna and Rovi, the Spanish pharmaceutical firm that distributes Moderna vaccines, have stated that the cause may be a manufacturing issue, and European safety inspectors have initiated an investigation.

Moderna stated that no safety or efficacy concerns were detected as a result of the incident.

Kanagawa prefecture said the vaccine’s domestic distributor, Takeda Pharmaceutical Co Ltd, had collected the vial with the suspected contaminant and that about 3,790 people had already received shots from the same lot.

More Moderna shots were temporarily halted in two other regions this week. In some cases, foreign substances have been found in unused vials, whereas others appear to be caused when bits of the vials’ rubber stopper break off when needles are incorrectly inserted.

Takeda did not immediately respond to a request for comment on the Kanagawa incident. The company posted a notice on its website on Wednesday saying that on rare occasions during manufacturing, rubber stopper material can get mixed into the vaccine solution.

Medical staff are advised to do a visual inspection of vials for discoloration or foreign materials before use, the notice said.

The contamination incidents come as Japan is battling its worst wave of infections, driven by the Delta variant, with daily infections exceeding 25,000 in August for the first time.

Severe COVID-19 cases are at record levels in Japan, leaving many people to recuperate at home amid a shortage of critical care beds. Only 45.4% of its population has been fully vaccinated, lagging vaccination rates of several developed countries.

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