By Kristen Holmes, Kaitlan Collins and Sara Murray, CNN

(CNN) -- Embattled Food and Drug Administration Commissioner Stephen Hahn met with White House chief of staff Mark Meadows for second day in a row on Wednesday as President Donald Trump remains frustrated no Covid-19 vaccine has been granted US emergency approval yet.

The previously unscheduled meeting comes as Trump and White House officials have grown increasingly upset with the FDA chief over the what they believe is a delayed approval of the coronavirus vaccine.

Agitation among administration officials grew overnight, after the United Kingdom became the first country to approve the Pfizer coronavirus vaccine for use.

A source familiar with internal coronavirus conversations said officials believe Hahn has had ample time to approve the vaccine. One person familiar with the President's thinking said part of his agitation is he wants to get as many people vaccinated as possible before he leaves office in order to get maximum bragging rights over this vaccine process.

"He wants to put out as many vaccines as possible between now and January," the person said. "He doesn't want (President-elect Joe) Biden to get any credit for it."

Speaking to reporters during the White House press briefing on Wednesday, press secretary Kayleigh McEnany said Hahn's meeting with Meadows was "par for the course."

"What I will say about Dr. Hahn is it is par for the course for the chief of staff to meet with him as we're trying to save American lives with the vaccine in record time," she said.

The FDA did not immediately respond to a CNN request for comment.

An FDA official expressed annoyance that the White House didn't seem to understand that there was a process.

"Let me be clear -- our career scientists have to make the decision and they will take the time that's needed to make the right call on this important decision," Hahn said in the statement.

Pfizer applied for the emergency use authorization November 20. Emergency use authorization from the FDA is not the same as full approval but allows products to be used under particular circumstances before all the evidence is available for approval, according to previous CNN reporting.

The FDA has previously said it has scheduled a meeting of its outside advisory panel to discuss Pfizer and BioNTech's application for emergency use authorization for a coronavirus vaccine for December 10.

Meadows and Hahn met for the first time Monday, after Meadows summoned him to the White House. Hahn requested their meeting happen over the phone, one source said, but was told by the White House that the chief of staff preferred to meet in person.