Johnson & Johnson said Wednesday said it may have found a problem with a batch of the drug substance for its COVID-19 vaccine.
The New York Times reported about 15 million doses were ruined, without citing a source.
They said the workers had conflated ingredients for the J&J vaccine and another produced at the same plant - a coronavirus vaccine developed by AstraZeneca.
J&J didn't directly respond to how many doses were ruined, but said in a statement that the the batch being produced at Emergent Biosolutions' site in Baltimore, did not meet quality standards and did not advance to the fill-and-finish stage.
They added that the problem at the plant which is not yet authorized to produce the drug substance for the vaccine was identified and addressed and alerted with the U.S Food and Drug administration.
The news coincides with the Biden administration trying to ramp up efforts to get vaccines out to U.S. states.
Last month the White House said it was exploring ways to increase manufacturing of J&J's vaccine.
Emergent, which is a manufacturer for both J&J and AstraZeneca, referred to J&J's statement when contacted for comment.