Johnson & Johnson released a statement Wednesday acknowledging that a batch of its Covid-19 vaccine doses handled by a manufacturing plant in Baltimore failed to meet quality standards, MarketWatch reports. J&J wouldn’t specify how many doses were affected, but the New York Times suspects the number to be around 15 million. 

“This quality control process identified one batch of drug substance that did not meet quality standards at Emergent Biosolutions, a site not yet authorized to manufacture drug substance for our Covid-19 vaccine,” the statement reads. “This batch was never advanced to the filling and finishing stages of our manufacturing process.”  

Politico reports workers at Emergent Biosolutions, which was among the 10 companies hired by Johnson & Johnson to manufacture the vaccine, accidentally mixed ingredients for the J&J dose with another manufacturer’s Covid-19 shot. Johnson & Johnson sought the Food & Drug Administration’s approval in enlisting Emergent with its distribution efforts, but this incident has caused a delay in the process. 

Despite the setback, Johnson & Johnson still believes it will not only meet its goal of delivering 100 million doses by the end of June and said it is “aiming to deliver those doses by the end of May.” J&J barely met its expectation of 20 million doses by the end of this month. This comes after the Biden administration reportedly expressed skepticism about their March plan after a shipment commitment in February wasn’t expected to be ready to be shipped until the second week of April, at the earliest. 

White House coronavirus coordinator Jeff Zients warned governors Tuesday to expect fluctuations in the number of doses received in the month of April. 

Read Johnson & Johnson’s entire statement below.