In an update over the weekend, J&J said it was increasing the ranks of manufacturing, quality and technical operations personnel to work at the Baltimore plant as it took over responsibilities for vaccine production.
Yet J&J reiterated its intention to deliver almost 100m doses of its vaccine to the US government by the end of May. The US has fully vaccinated 61m people, of which 4m received J&J's single-dose jab, according to the US Centers for Disease Control and Prevention.
Emergent's Baltimore plant has not yet secured emergency authorisation from the US Food and Drug Administration to manufacture substances for the vaccine, and J&J said it would work towards that goal.
AstraZeneca said it was working with the federal government to carry out plans to produce its vaccine in the US. "As part of that effort, and in full co-operation with the US government, AstraZeneca will relocate production" of its vaccine drug substance from the Emergent facility, it said.
The moves came after the Biden administration put J&J in charge of the Baltimore plant and moved to stop it from making the AstraZeneca vaccine, the New York Times reported, citing senior federal health officials.