British-Swedish drugmaker AstraZeneca drew a sharp rebuke from the European Union after the company said late last month it would cut EU supplies of its COVID-19 vaccine in the first quarter.

EU leaders lashed out at the company for not honoring its contractual obligations, with some accusing it of diverting vaccines produced in the bloc to other countries. AstraZeneca, which has developed the vaccine in cooperation with the University of Oxford, has denied the charges, blaming the supply cut on production issues.

The spat comes at a time the EU’s vaccination drive is faltering and the bloc is taking much flak for trailing the United States and the United Kingdom in getting shots into the arms of its citizens. EU members, including Germany and France, are facing supply shortages, which has forced authorities in some regions to delay or suspend vaccinations. The EU has responded by introducing export controls on coronavirus vaccines to monitor doses leaving its shores.

AstraZeneca has agreed to supply to the EU only around half of the 80 million doses it had committed to deliver during the first quarter.

Why did AstraZeneca cut vaccine supplies?

The production of AstraZeneca’s vaccine broadly involves two steps: one is producing the actual vaccine or drug substance, and the other is putting the vaccine into vials. Those two steps can take up to 60 days each.

AstraZeneca has said while it’s facing no issues with the second step, it’s struggling to produce high quantities of the vaccine at an EU production plant.

“Essentially, we have cell cultures, big batches, 1,000-liter or 2,000-liter batches. We have cell cultures inside those batches, and we inject them with the virus, the vaccine if you will. Those cells produce the vaccine — it’s biotechnology protection,” AstraZeneca CEO Pascal Soriot told Italian newspaper La Repubblica last week. “Now, some of those batches have a very high yield and others have low yield. Particularly in Europe, we had one site with large capacity that experienced yield issues.

“The yield varies from one to three, by the factor of three. The best site we have produces three times more vaccine out of a batch than the lowest producing site,” he added 

Soriot also said the company faced similar glitches in other countries, including in the UK, but was able to sort them out because it had more time given that London had signed its contract three months before the EU.

AstraZeneca’s European supply chain

AstraZeneca has partnered with several contract manufacturers across the EU to scale up the production of its COVID-19 vaccine. The vaccine, or the drug substance, is currently being produced at two facilities in the Netherlands and Belgium. It’s the company’s Belgian partner, Novasep, which has struggled with low yields.

The vaccine is then filled into vials and packaged in Dessau in eastern Germany by IDT Biologika and by Catalent in Anagni, Italy. Spanish pharmaceutical group Insud Pharma will also undertake vial filling and packaging services for the vaccine in Spain’s Castilla-La Mancha region.

Russian pharma company R-Pharm’s German unit has also signed up to produce the vaccine at its site in Illertissen in southern Germany. China’s Wuxi Biologics could potentially use a former Bayer factory in Wuppertal, Germany, to manufacture the vaccine.

AstraZeneca plans to deliver up to 3 billion doses across the globe by the end of this year. The EU has made a €336 million ($404 million) down payment to secure up to 400 million doses of the vaccine, which was approved by the EU’s drugs regulator last week.

How are other vaccine makers faring?

Pfizer and BioNtech are also struggling to stick to their delivery commitments due to production and supply chain problems. But the EU has said that unlike AstraZeneca, the companies are distributing the impact of the disruption fairly among buyers.

Several European governments confirmed last month that Pfizer-BioNtech would temporarily cut shipments of its vaccine due to “modifications” at its Puurs plant in Belgium.

On Monday, the companies promised to deliver up to 75 million more doses to the EU in the second quarter. The companies said they would increase production with a new facility set to open in the German city of Marburg in February. The facility will have the capacity to produce 750 million vaccine doses each year.