Emergent BioSolutions said Thursday it will resume manufacturing bulk drug substances for Johnson & Johnson's COVID-19 vaccine after an extensive review prompted by the ruining of millions of doses at one of its plants.

The company said it was working with the U.S. Food and Drug Administration and Johnson & Johnson to address quality concerns.

In April, the FDA asked the company to halt production of materials at its Baltimore facility for COVID-19 vaccines after a mix-up of ingredients for Johnson & Johnson's vaccine and AstraZeneca's.

Since then, Johnson & Johnson has installed its own expert technicians and Emergent developed a plan to address quality control issues.

"The American people should have high expectations of the partners its government chooses to help prepare them for disaster, and we have even higher expectations of ourselves," Emergent CEO Robert Kramer said in a statement. "We have fallen short of those lofty ambitions over the past few months, but resumption of manufacturing is a key milestone, and we are grateful for the opportunity to help bring this global pandemic to an end."

Baltimore's WJZ reported that FDA inspectors spent a week at the factory, reviewing security camera footage that captured employees carelessly handling vaccine materials. Among the issues inspectors discovered were unsanitary conditions and poorly trained employees, the station reported.

Emergent's Baltimore plant can resume production, but the FDA will inspect individual lots of vaccines before they can be shipped and administered, CNN reported. The FDA authorized the fifth batch of the one-dose Johnson & Johnson vaccine to be shipped on July 13 but did not indicate how many doses would be included.

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