It would be shooting itself in the foot to admit the vaccines it had bought in a group-buy scheme were ineffective or in any way sub-standard. Member states would be furious, and Ursula would have been gone.
This article has a summary of statements from different politicians - https://news.sky.com/story/covid-19-what-eu-leaders-said-abo... The closest I can see for the EC is one from Ursula, with the article reporting:
"She then suggested the UK had compromised on "safety and efficacy" by approving the jab so early, despite the EMA reaching the same conclusions as the UK's internationally-respected MHRA which approved the vaccine."
(That is realistically just her attempts to excuse a slower approval process that ultimately reached exactly the same outcome)
Happy to be proved wrong though.