Pfizer will only ship half the number of COVID-19 vaccine doses it initially projected for this year due to supply chain issues, the Wall Street Journal reports. “Scaling up the raw material supply chain took longer than expected,” a company spokesperson said, adding that their clinical trial finished later than expected. Pfizer now projects to ship 50 million doses worldwide this year. “Some early batches of the raw materials failed to meet the standards,” an anonymous source involved with the creation of the vaccine told the Journal. “We fixed it, but ran out of time to meet this year’s projected shipments.”

The U.K. approved Pfizer’s vaccine for emergency use on Wednesday. The U.S. is expected to roll out the Pfizer vaccine this month, pending review by the FDA, as well as a separate vaccine developed by Moderna. A third vaccine, produced by Oxford University and AstraZeneca, is not expected to be ready for FDA approval until late January, according to CNBC.