A manufacturing mishap in a Baltimore manufacturing plant contracted to produce the single-shot Johnson & Johnson COVID-19 vaccine has ruined 15 million doses and will delay shipments while U.S. regulators investigate.

Workers at the Baltimore-based Emergent BioSolutions plant conflated vaccine ingredients a few weeks ago, causing about 15 million doses of vaccine to go to waste, the New York Times reported Wednesday.

The mishap has caused a temporary halt in production until the Food and Drug Administration completes its investigation and gives the green light to resume making the shots. Tens of millions of doses, making up all further shipments of the Johnson & Johnson vaccine, were slated to come out of that Baltimore plant.

Federal officials say the unexpected shipment delays will not affect Johnson & Johnson’s ability to fulfill its commitment to help supply the U.S. government with enough vaccine to immunize every adult by the end of May.

The Johnson & Johnson vaccine was authorized for public use by the FDA in February. It is the first single-dose COVID-19 vaccine to enter the market and is much easier to store and transport than other vaccines because it doesn’t require ultra-cold temperatures to keep it viable for up to three months. The introduction of the single-shot vaccine has sped up vaccinations and been proven a more sensible option for hard-to-reach parts of the country where access to ultra-cold storage is limited.

Production hiccups earlier this year caused an initial shortfall, but the company is on track to fulfill its deal with the federal government for 100 million shots by the end of June.

To date, more than 150 million shots have been administered in the United States at a daily rate of more than 2.8 million doses, according to a Bloomberg tracker. Nearly 55 million people have been fully vaccinated, putting the U.S. on track to vaccinate 75% of the adult population in the next four months.

Original Location: Johnson & Johnson vaccine shipments to be delayed after production mix-up ruins 15M doses