An estimated 30 million to 50 million doses of Johnson & Johnson's Covid-19 vaccine made early this year sits 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 release of those doses. The agency must still inspect and authorize 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.

The FDA in April halted operations at Emergent's production facility after J&J's vaccine was found to be contaminated with material from AstraZeneca's Covid-19 shots, which were also being manufactured there at the time.

The contamination ruined about 15 million J&J doses and set back its US vaccine rollout by weeks.

Material manufactured for the J&J vaccine at the Baltimore plant prior to the April shutdown and awaiting FDA approval could be enough to produce as many as 50 million shots, the two sources said. They asked not to be named because they were not authorized to speak publicly on the issue.

Of the 100 million doses worth of vaccine material Emergent described in an April Congressional hearing as being sidelined, the FDA has so far cleared nine batches of J&J's vaccine and three batches of AstraZeneca's. It has not disclosed how many doses were in those batches.

Emergent in late July said it would resume production of J&J's vaccine at the plant following additional FDA reviews, but has not provided updates on production or timing of potential shipments. L1N2P535Q

Emergent has begun making new vaccine substance, but the FDA has yet to provide guidance on when it plans to inspect the Baltimore facility, one of the sources said.

The FDA said in a statement that it conducted a limited inspection of Emergent's facility in July to confirm it had conducted corrective actions following the April production pause. A previous inspection had turned up a raft of sanitary, safety and bad manufacturing practice issues at the plant. 

The agency said it has not yet authorized the facility to ship doses and continues to review batches made prior to the production halt. It has based its batch approvals on reviews of facility records and quality testing conducted by the manufacturer.

The FDA typically waits for a drug manufacturing facility to produce multiple batches of its product before conducting an inspection, according to a former FDA official who asked not to be named because she was not authorized to speak with the media.

Following the Emergent plant shutdown, J&J lowered its production target for 2021 to between 500 million and 600 million doses from around 1 billion. It expects to be able to make 1 billion doses annually starting next year. 

J&J has not specified whether it needs Emergent to restart production to hit its 2022 target. It has another manufacturing facility in Leiden, Netherlands, and production agreements with other contract manufacturers, including Catalent Inc and India's Biological E.

The United States contracted with J&J for 100 million shots in 2020 and ordered an additional 100 million in March.

Last week, the FDA authorized J&J's vaccine as a booster for people who are already vaccinated but desire additional protection against COVID-19, including anyone over age 18 who originally received the company's single-dose shot.

Use of J&J's vaccine fell sharply in the United States after it was linked to a rare but potentially lethal blood clotting disorder.