An estimated 30 million to 50 million doses of Johnson & Johnson's Covid-19 vaccine made early this year sit idle in Emergent BioSolutions Inc's plant in Baltimore awaiting a green light from US regulators to ship, two sources familiar with the matter said.

Emergent, a contract drug manufacturer, is waiting for the US Food and Drug Administration to approve the release of those doses. The agency must still inspect and authorise the plant before Emergent can ship newly manufactured drug substance, one of the sources said.

The exact number of doses sitting idle cannot be determined, the source said, because Emergent only makes raw vaccine substance and does not fill vials with finished product.

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