EU chief Ursula von der Leyen said on Friday that Pfizer's CEO had guaranteed the delivery of all doses of the coronavirus ordered by the bloc for the first quarter of 2021.
"I got, like many of you, the news today that Pfizer announced delays," von der Leyen said at a press conference in Portugal.
"I immediately called the CEO of Pfizer and he explained that there is a production delay in the next weeks, but he reassured me that all guaranteed doses of the first quarter will be delivered in the first quarter."
The pharmaceutical giant admitted on Friday that it expects lower coronavirus vaccine deliveries for a stretch beginning in late January as it scrambles to lift output later this winter and throughout 2021.
It said shipments would be affected until into early February as it seeks new regulatory approvals for its manufacturing processes aimed at ramping up output.
Six EU health ministers signed a letter to the European Commission on Friday to express "severe concern" over the delivery delays for the coronavirus vaccine developed by BioNTech and Pfizer.
Von der Leyen said Pfizer's boss was "personally on the case on reducing the delay period, and to make sure that they will catch up as soon as possible."
"That was very important to convey the message to him that we urgently need the guaranteed doses."