TOKYO — The Japanese health authorities on Thursday announced that they would halt the use of over 1.6 million doses of Moderna’s coronavirus vaccine after some vaccination sites reported finding tainted vials.
The problem comes as Japan, which initially struggled to get its vaccination program into full gear, confronts its worst wave of Covid-19 cases since the pandemic began, raising concerns that medical systems in some parts of the country could be overwhelmed.
Unspecified contaminants were discovered in nearly 40 doses of the vaccine at eight locations across Japan, prompting the decision to pull the lot that included them, as well as two other lots produced at the same location, the public broadcaster NHK reported.
In a statement, Takeda Pharmaceutical, the company that distributes the shots in Japan, said that it had asked Moderna to carry out an urgent investigation into the cause of the problem. Takeda did not report any concerns about health issues arising from use of the tainted vials.
Speaking to reporters on Thursday, the chief cabinet secretary, Katsunobu Kato, said that an unknown number of people had been vaccinated with the contaminated doses, but that the government had received no reports of ill effects. He urged people with concerns to consult their doctors.
After getting off to a slow start, Japan is now administering over a million vaccine doses each day. Currently, about 43 percent of the population is fully vaccinated. In addition to Moderna, Japan has approved the use of vaccines produced by Pfizer and AstraZeneca.
However, as the inoculation program has accelerated, so has the virus. Tokyo declared its fourth state of emergency in July as it confronted a rapid rise in cases driven by the Delta variant. The situation has since deteriorated rapidly, with daily case numbers reaching over 25,000 for the first time on Friday. Total deaths are at nearly 15,700.
The decision to withdraw the Moderna doses is not expected to have a major impact on the overall vaccination program, Mr. Kato said, adding that the government was working to reduce any disruptions.
Despite the rising numbers, Tokyo has carried on more or less as usual. The city is currently hosting the Paralympics, which opened on Tuesday.
Much like for the Olympics, which were held for two weeks starting at the end of July, the organizers of the Paralympic Games have adopted strict measures — such as daily testing of athletes — to try to keep infection rates down. Since Aug. 12, 184 people associated with the Paralympics have tested positive for Covid-19. On Thursday, Japanese news media reported that an athlete had been hospitalized with the virus, which would be a first for the event.