Mario Tama/Getty Images

About 15 million doses of Johnson & Johnson's one-dose COVID-19 vaccine were spoiled when workers at a Baltimore plant accidentally mixed up ingredients, The New York Times reported on Wednesday, delaying future shipments of the vaccine.

The error took place several weeks ago, the Times said, at a plant run by Emergent BioSolutions, which is a manufacturing partner to Johnson & Johnson and AstraZeneca. The Food and Drug Administration is now investigating the matter.

The Johnson & Johnson doses that are now being used to vaccinate Americans were manufactured in the Netherlands, but all future doses were slated to come from Baltimore, the Times reports. People with knowledge of the matter said those shipments are now in question, but with Pfizer and Moderna still delivering their vaccines, federal officials think there will be enough doses available to vaccinate every American adult by the end of May.