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Boxes of the Johnson & Johnson COVID-19 vaccine at the McKesson Corporation in Shepherdsville, Kentucky, on March 1, 2021.POOL New/The Associated Press

Federal U.S. regulators have told Johnson & Johnson that about 60 million doses of its coronavirus vaccine produced at a troubled Baltimore factory cannot be used because of possible contamination, according to people familiar with the situation.

The U.S. Food and Drug Administration plans to allow about 10 million doses to be distributed in the United States or sent to other countries, but with a warning that regulators cannot guarantee that Emergent BioSolutions, the company that operates the plant, followed good manufacturing practices. The agency has not yet decided whether Emergent can reopen the factory, which has been closed for two months because of regulatory concerns, the people said.

The Johnson & Johnson doses administered in the United States so far were manufactured at the firm’s plant in the Netherlands, not by Emergent.

More than 100 million doses of the Johnson & Johnson vaccine and at least 70 million doses of the AstraZeneca vaccine were put on hold after Emergent discovered in March that its workers had contaminated a batch of Johnson & Johnson’s vaccine with a key ingredient used to produce AstraZeneca’s.

Johnson & Johnson’s vaccine was once considered a potential game-changer in the nation’s vaccine stock because it required only one shot and was particularly useful in vulnerable communities. But the U.S. government now has an ample supply of the vaccines from Pfizer-BioNTech and Moderna, the two other federally authorized vaccine developers, and no longer needs Johnson & Johnson’s supply.

Still, the loss of 60 million Johnson & Johnson doses puts a dent in the Biden administration’s plan to distribute vaccines to other countries.

The FDA’s plan to allow 10 million doses to be used in the United States or abroad with a warning is somewhat unusual for a product under emergency authorization, experts said. Regulators have the discretion to take that action if the drugs are badly needed and in short supply, they said.

Representatives from Johnson & Johnson and Emergent declined to comment on the agency’s decision.

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