Boris Johnson has told a private meeting of Tory MPs that the success of the UK's Covid vaccine programme was because of "capitalism" and "greed".
But sources said the prime minister had "very insistently" withdrawn his comments straight after making them during a Zoom call with backbenchers.
The remarks were not connected to the EU row over vaccine supply, they added.
A government source said the PM was referring to the profit motive driving companies to develop new products.
The PM also reportedly praised work by large drug companies during the pandemic.
The prime minister's full remarks, which first appeared in the Sun newspaper, were reported to be: "The reason we have the vaccine success is because of capitalism, because of greed, my friends."
Wales Office Minister David TC Davies, who attended the meeting, said Mr Johnson "made it absolutely clear it was a joke - a reference to the film Wall Street".
He added: "Whoever leaked that needs to take a long hard look at themselves because it was very irresponsible."
The remarks came as some 28.3 million people in the UK - more than half the adult population - have had at least a first dose of either the Oxford-AstraZeneca or Pfizer vaccines.
But the latest figures show jabs being administered across the EU at less than a third of the rate achieved so far in the UK.
Over the last few days, Mr Johnson has been speaking to European leaders in an effort to dissuade them from imposing an export ban on Oxford-AstraZeneca vaccine exports to the UK when they meet on Thursday.
One MP told me the prime minister's "greed" comments had been intended to poke fun at the chief whip, who was gobbling his cheese and pickle while sitting next to him during the meeting.
Believe it or not, the Conservative Party's boss of discipline, Mark Spencer, has been christened with the nickname "Big Farmer", like "Big Pharma" - the pharmaceutical companies.
And it's vehemently denied that the PM's comments were designed to stir up anything in the row with the EU.
Sources are adamant that Mr Johnson was not intending to be critical of the pharmaceutical companies in any way.
During the MPs' committee meeting, Mr Johnson praised AstraZeneca for providing vaccines in the UK at cost.
One of those who attended said they had never seen anyone withdraw a comment "so fast or so vehemently" as the prime minister's one on procurement.
Mr Johnson "realised he had messed up as soon as he had said it, and didn't mean it", the MP added.
Several sources said he had asked those present to "remove that comment from your collective memory".
It is understood the prime minister did not compare the UK's vaccination efforts with those of EU countries during his address.
In his Budget earlier this month, Chancellor Rishi Sunak announced an extra £1.65bn to help reach the target of offering a first dose to every UK adult by 31 July.